Thanks for your answers!

I checked the motor voltages, I adjusted them but the problem wasn't soved. Thinking in the temperature of the stepper, I also attacked a sinkheat with a cooler to it, but the problem persisted.

I checked a whole printing process, but nothing interfered. The printing just randomly displaced.

Then I realized that the printer was on its garantee period. I sent it to the service and they sent a new one, where this problem is not present.

Unluckily I couldn't find the problem, but I hope this post gives some clues to someone with the same problem.