Hello again!
I did everything as you said, first with a complete clean up of the printer, then tightened the set of screws and finally dropped some oil on the 6 rods in the gantry. Also the firmware has been updated.
I've done some printing and the problem now seems to be completely random, some of the prints turn out perfectly while others present the same issue, I've noticed that the problem happens with the brim, which are the first layers. So I'm starting to think that it's due to a software of firmware problem.
What else can be done?