So I started to make my own sound fonts in 16bit/22050Hz.
I copy my sound banks to my desktop and format the SD card.
I keep one original Meat on the NB v3 and put the custom one in the other bank.
The original is still fine, but when I try to boot the other sound bank, it gives the standard first beep
and instead of the boot sound it beeps one time again and doesn't play any of the other sounds when I power on or off.
It does keep the time in mind which I put in the config file, meaning when I power on, I have to power off again before I can switch fonts again, only it is silent.
After that, the original Meat works just fine.

Does anyone know what the problem could be?
All files are there, maybe some meta data?
The sounds are bigger than the original sound fonts, but I don't think that could be a problem