It is very difficult to debug because it's a sporadically error.
I think i have to begin at the beginning and debug it.
But ATM time is short.
If i run the Pi on PSU, the kernel-dumps are gone but flickering is still there.
There are 2 different problems.
Problem1: Kernel-Dumps and Undervoltage.
Problem2: USB-Bus runs on limit with 2 cameras (i think).
Flickering is also there with only 1 Camera. uvcvideo option quirks does not help.
Still no kernel-dumps with PSU attached.