Happy Thanksgiving Bizuth_74!
I will just throw in some brainstorming to move this along and respond for support...do you have another of the same FC to prove that it can be leveled/done on your bench exactly as the first? If so do it.
Also, is the FC in question installed/seated into a case that is completely snapped closed on all four corners?
How do you hold it down to the bench? Finger hold, mounting tape, loosely/not fixed?
What is the distance between the FC and the closest iron/metal object/s, speakers, transformer, power supply, monitor, PC?
ISOLATE at least 24" placed on surface/structure of non-metallic material. 24" Not a magic number just insurance.
Could be a bad gyro/thingy.
Do not be discourage, only challenged.
Good problem solving to ya,
West