So at yesterday's rehearsal, I saw that the led diode's (and LCD screen) of my remote were a lot less bright than the ones on the two other remotes (bassplayer and other guitarist).
I mean, the difference is actually huge. In bright sunlight they would probably be barely visible.
We did some testing, and here is the baffling part:
my kemper + my ethernet cable + my remote --> dim leds/lcd screen
my kemper + another ethernet cable + my remote --> dim leds+lcd screen
my kemper + my ethernet cable + another remote --> bright leds/lcd screen (so it's not the PoE of my kemper)
another kemper + my ethernet cable + my remote --> bright lights/lcd screen (so it's not my remote either!)
So as you can see, the issue is really the combination of my remote with my kemper.
Went to system settings and everything is set correctly regarding remote brightness and such.
The other kemper were my remote is working correctly on, has the same OS as mine.
No idea where to start looking for a solution