Issues with Octoprint Wifi Connection

What is the problem?
I have a strange Issue when I try to connect to Octoprint that is connected via Wifi Connection only.
No connection can be established.

I have assigned a fixed IP for the LAN Connection of Octoprint and another one for the Wifi Connection. Octoprint, in the latest version, runs in a Pi 3B+.
I can see in my Router that the Wifi and LAN Connection is established and I can ping both of them when the LAN Cable is attached.
I can also open the Octorpint UI via both fixed IP-Addresses (Octoprint.local doesnt work anymore since I have updated to the latest Version)
As soon as I disconnect the LAN Cable both IPs cant be pinged anymore (one is obvious) and the Web UI doesnt work anymore, even I can see in the Router the Wifi Connection to the Pi is still established.

What did you already try to solve it?
My thinking was the Wifi Signal not strong enough so Im thinking to add a USB Wifi Antenna that will be routed outside of the metal Electronics Cabinet. But even with open Cabinet it doesnt work.

Logs (syslog, dmesg, ... no logs, no support)
octoprint.log (389.3 KB)
serial.log (148 Bytes)

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, ...)

That is a common problem on the Pi. You have to set the priority of the network interfaces. Normally eth0 is a higher priority than wlan0. Once you disconnect the Ethernet cable, everything is still looking to eth0 as the default route