Wifi Power Management issue

What is the problem?
I have a Raspberry Pi3 running Octopi in my garage. It's connected to the Lan via Ethernet cable and works flawlessly. I wanted a hotspot in the garage too so after looking up a solution I installed Hostapd, followed instructions and yes, now I have a hotspot. Everything works fine for a couple of minutes then the Hotspot disapears, but only if I'm not actively using the connection... It also remains working if I am connected via SSH.

What did you already try to solve it?
I've discovered that the RasPi3 has engerystar power management on by default and I'm guessing that this is the root cause. I can successfully switch it off at the command line with "iwconfig wlan0 power off" which works until a reboot, then it's back to it's default ON status. Forums say that this command can be added to the /etc/rc.local file which I have done but this does not work. I always have to type it in at the command line (after connecting via SSH).

So my question is, in Octopi how do you permanently disable ALL power management features?

Logs (syslog, dmesg, ... no logs, no support)

Octoprint Systeminfo bundle uploaded here:

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, ...

I have 1 router that is the main hub for my network. The Octopi hostap in bridge mode connects over a Powerline Ethernet cable to provide an Access Point to the Lan. Everything works as expected, it's just the timeout of the powermanagement coming on I have an issue with.

a simple method:
sudo crontab -e

then add:

@reboot iwconfig wlan0 power off

then save...