The stick works well, even in Master mode, but it get's extremely hot, just by being active. I just let it connected for 30 min and could barely hold it. I fear the plastic cover could melt.
I tried connecting it with a usb extender cable, connecting it to a powered usb hub and also reduced maximum transmit power to 0. Nothing changed anything.
Could this be a driver issue?
Install a fan.. 
What is the searchable model number of the USB device?
What is the ambient room temp in it's location?
Could be since the chips working creating the heat.
057c:84ff AVM Berlin FRITZ!WLAN USB Stick N
Room Temperature is currently 27.7°C.
I found it in my drawer. Just measured it and it got to 50°C in 5 min just by beeing powered. Even without driver installed. On my windows PC it does not get so hot.
I'll try with rice.
Extender could be good idea just to move heat away from your computer or whatever it is plugged into?
Also how hot is too hot I wonder? Probably hotter than too hot to touch. I had a metal usb drive and it got too hot to touch but ran fine for ages.
Have you measured the same high temperature when the USB stick is connected to a different OS (windows for example)?
Do you experience any issues due to the high temperature (e.g. stick stops working)?
If yes: Contact AVM, report your issue, get a new USB stick.
If no: Contact AVM, report your high temperature issue, wait for reply.
Looks like it get's similarily hot under windows.
I didn't do any long term tests yet, I was afraid that it will die. On the other hand it's not used anyway. If it dies it dies.
The stick is like 15 years old, I doubt, I'll get a new one.
EDIT: I just tried to actively use it and the connection does not stay stable after a couple of minutes. Maybe I'll try @Lynx's idea 
