Best posts made by AfanasevSA

To use 24V fans, you should left V_FAN and VIN shorted with jumper, as photo.

@Danal, thanks for your answer, it's almost full. Interesting about belts. The same technique for boards - use star topology, don't route wide loops for single ended signals (ground is a return path for single ended signals), be careful with long high impedance lines and so on. This is EMC and it's cool.
I want not only to eliminate the problem, but to find the reason, the most EMC-sensitive line.
So, my first question from previous post is still actual. I'll try some solutions and post the result here. Maybe my 5 cents will be useful for colleagues, maybe not, but the result is interesting.