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OctoPi doesn't show up on one device, but is accessible with a different device

What is the problem?
At times, my brother's or my workstation cannot access the OctoPi (running on a 3B on Wi-Fi at 10.0.0.3, a reserved DHCP address). Most of the time, my brother cannot access the OctoPi. I run a ping to the OctoPi's IP address and it comes back as unreachable. On my machine, it's accessible. If I SSH into the OctoPi and ping my brother's machine, it will eventually connect and starts working. I'm aware that the Pi is undervolting, even though the power supply that I had bought it with is intended for the Pi 3B. After some looking, it might have to do with ARP, but I'm unsure on how to fix the issue. The octopi.local address often doesn't work.
What did you already try to solve it?
So far, I've tried logging into the OctoPi to ping my brother's workstation in order for ARP to catch up but this isn't a permanent solution.
Logs (syslog, dmesg, ... no logs, no support)
octoprint-systeminfo-20220514133529.zip (325.0 KB)

Additional information about your network (Hardware you are trying to connect to, hardware you are trying to connect from, router, access point, used operating systems, ...)
OctoPi is running on a Pi 3B using Wi-Fi on the 2.4GHz band, it has a strong signal strength.
The workstations accessing it is an:
HP Z420 Workstation running Fedora Linux connected via Wi-Fi 5GHz (10.0.0.87)
Lenovo Ideacenter (unknown model) running Windows 10 connected via Wi-Fi 5GHz (10.0.0.50)
Router and Access Point is an Xfinity xFi Gateway.
Network address is 10.0.0.0 with a subnet mask of 255.255.255.0. The OctoPi's IP is 10.0.0.3 and it is reserved in DHCP.

Since you have an RPi 3B, you don't have a choice of WiFi bands, it must be on 2.4GHz. On the other two machines on 5GHz, you should have a choice. What happens if all three systems are connected to the 2.4GHz band?

Can you provide the output of ifconfig on the RPi and Linux server and ipconfig /all on the Windows system? Output of arp (it may be arp print) on each system would be helpful as well.

Because of the way the network shows up via Wi-Fi, it only shows as one SSID for both bands. I've found instructions for how to force it to 2.4GHz under Windows but I can't easily find instructions for Linux. For the MAC addresses, I have added x's to the address to censor the full address.
IPv6 addresses have been removed.
Also to mention, my brother uses the Octoprint Cura plugin. Not sure if this has anything to do with it, but it's good to mention.

Here are the ifconfig and arp outputs on the RPi: (the arp output of which looks suspect)

wlan0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 10.0.0.3  netmask 255.255.255.0  broadcast 10.0.0.255
        ether b8:xx:xx:xx:xx:1f  txqueuelen 1000  (Ethernet)
        RX packets 1812174  bytes 305350991 (291.2 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 8497951  bytes 3704937364 (3.4 GiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
Address                  HWtype  HWaddress           Flags Mask            Iface
10.0.0.1                 ether   1c:xx:xx:xx:xx:0b   C                     wlan0
10.0.0.50                        (incomplete)                              wlan0
10.0.0.87                ether   44:xx:xx:xx:xx:64   C                     wlan0

On my Fedora workstation:

wls1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 10.0.0.87  netmask 255.255.255.0  broadcast 10.0.0.255
        ether 44:xx:xx:xx:xx:64  txqueuelen 1000  (Ethernet)
        RX packets 13906932  bytes 18361071618 (17.1 GiB)
        RX errors 0  dropped 87  overruns 0  frame 0
        TX packets 5227091  bytes 570167321 (543.7 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
Address                  HWtype  HWaddress           Flags Mask            Iface
10.0.0.74                        (incomplete)                              wls1
10.0.0.68                ether   20:xx:xx:xx:xx:3e   C                     wls1
10.0.0.219               ether   f4:xx:xx:xx:xx:08   C                     wls1
10.0.0.84                ether   38:xx:xx:xx:xx:60   C                     wls1
10.0.0.209               ether   20:xx:xx:xx:xx:2d   C                     wls1
10.0.0.114               ether   20:xx:xx:xx:xx:be   C                     wls1
10.0.0.0                         (incomplete)                              wls1
10.0.0.147               ether   b8:xx:xx:xx:xx:ec   C                     wls1
10.0.0.22                        (incomplete)                              wls1
10.0.0.187               ether   fa:xx:xx:xx:xx:27   C                     wls1
10.0.0.50                ether   60:xx:xx:xx:xx:bf   C                     wls1
10.0.0.54                ether   98:xx:xx:xx:xx:24   C                     wls1
10.0.0.67                        (incomplete)                              wls1
10.0.0.111               ether   1c:xx:xx:xx:xx:35   C                     wls1
10.0.0.134               ether   34:xx:xx:xx:xx:e1   C                     wls1
_gateway                 ether   1c:xx:xx:xx:xx:0b   C                     wls1
10.0.0.3                 ether   b8:xx:xx:xx:xx:1f   C                     wls1

On my brother's Windows 10 workstation:

Wireless LAN adapter Wi-Fi:

   Description . . . . . . . . . . . : Realtek 8821AE Wireless LAN 802.11ac PCI-E NIC
   Physical Address. . . . . . . . . : 60-XX-XX-XX-XX-BF
   DHCP Enabled. . . . . . . . . . . : Yes
   Autoconfiguration Enabled . . . . : Yes
   Lease Obtained. . . . . . . . . . : Saturday, May 14, 2022 12:54:17 AM
   Lease Expires . . . . . . . . . . : Thursday, May 19, 2022 5:42:53 PM
   IPv4 Address. . . . . . . . . . . : 10.0.0.50(Preferred) 
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Lease Obtained. . . . . . . . . . : Saturday, May 14, 2022 12:54:16 AM
   Lease Expires . . . . . . . . . . : Tuesday, May 17, 2022 5:26:08 PM
   Default Gateway . . . . . . . . . : 10.0.0.1
   DHCP Server . . . . . . . . . . . : 10.0.0.1
   DNS Servers . . . . . . . . . . . : 8.8.8.8
                                       8.8.4.4
   NetBIOS over Tcpip. . . . . . . . : Enabled

A note about the arp -a output, before pinging the machine from the RPi, the RPi's IP & MAC address didn't show up in this list. After pinging it, it shows in this list. After about an hour to a few hours, the ARP entry grows stale and eventually stops working until the Pi pings his machine again.
This is what happens when it cannot connect anymore, the ARP entry for the RPi disappears.

Interface: 10.0.0.50 --- 0x13
  Internet Address      Physical Address      Type
  10.0.0.1              1c-xx-xx-xx-xx-0b     dynamic   
  10.0.0.2              a0-xx-xx-xx-xx-a0     dynamic   
  10.0.0.54             98-xx-xx-xx-xx-24     dynamic   
  10.0.0.67             f8-xx-xx-xx-xx-3b     dynamic   
  10.0.0.68             20-xx-xx-xx-xx-3e     dynamic   
  10.0.0.76             f0-xx-xx-xx-xx-c9     dynamic   
  10.0.0.87             44-xx-xx-xx-xx-64     dynamic   
  10.0.0.111            1c-xx-xx-xx-xx-35     dynamic   
  10.0.0.134            34-xx-xx-xx-xx-e1     dynamic   
  10.0.0.209            20-xx-xx-xx-xx-2d     dynamic   
  10.0.0.219            f4-xx-xx-xx-xx-08     dynamic   
  10.0.0.255            ff-ff-ff-ff-ff-ff     static    

I think one of the issues is DNS. My router's DHCP server updates a local DNS server and hands out that server to DHCP clients. I forgot to ask for DNS info but the Windows system shows that it is using global DNS (Google if I remember right).

Please show the output of /etc/resolv.conf on the RPi and Linux server. I think the router has a web interface (try admin and password or contact Xfinity for help).

Yeah, I see that my brother (or past me at some point) put Google's DNS onto his workstation. I'll try setting it back to the one handed out by DHCP.
RPi's /etc/resolv.conf:

# Generated by resolvconf
domain hsd1.[xx].comcast.net
nameserver 75.75.75.75
nameserver 75.75.76.76

My workstation's /etc/resolv.conf (which, in the file says to use resolvectl status to see uplink DNS servers):

Link 3 (wls1)
    Current Scopes: DNS LLMNR/IPv4 LLMNR/IPv6
         Protocols: +DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 2001:558:feed::1
       DNS Servers: 75.75.75.75 75.75.76.76 2001:558:feed::1 2001:558:feed::2
        DNS Domain: hsd1.[xx].comcast.net

Yes, the router does have a web interface, it sets Comcast's DNS server by default.

I have also edited the arp -a output in post 3, which shows the ARP entry disappearing when it can no longer connect.

Changing the DNS from the global Google servers to the global Xfinity servers doesn't fix the problem. Your local network wants to resolve the names of the local systems and can't because they don't exist in the global DNS namespace. Your local DHCP server can't add names if you aren't running a local DNS server.

I believe you need to create host files on each local system that contain the local name to local IP translations. See http://www.steves-internet-guide.com/hosts-file/ for assistance if you need it.

If this doesn't fix the problem, then you may have to (install and) use TCPDUMP on the RPi to capture ARP, DNS, and HTTP traffic when your brother tries to connect to the RPi and fails. You could also install Wireshark on his system and capture the same information.

Last possibility is an IPV6 issue. Since you have edited out most of that information, I'm afraid I can't suggest anything. Perhaps the dump files will give you some insight.