Okay I hope I finally found what caused the issue that I constantly lost the connection to homey:
After a long time of trial and error (changing my ASUS rt-ax88u router settings), I think I found the issue in a setting called ‘Smart Connect’:
Once disabled Homey didn’t went ‘offline’ anymore
Kind of strange, cause homey only supports 2.4Ghz, so it can’t hop/toggle from one band to another. Maybe I’m wrong and I changed some other settings as well that might fixed the issue 
