Problem with sudden random offset

Hi folks,

I've made a custom repstrap and I encounter some recurring problem.

When printing, it sometime offsets the whole print both in Y and in X axis from a huge amount of steps.
It isn't a overheating problem since everything is cool (I put fan on each motor and on the driver and I can run a 3 hours print without problem which means the nominal temperature is cool enough).

It happens randomly, sometimes after 5 minutes, other times after 2 hours ...

I think it could be software related since I drip feed through USB.
I'm using a Megatronics V1.0 with Marlin and I've a spare LCD display so I could try to print in autonomous mode (would still need a keyboard).

what do you think ? (I'm adding a picture so you can see what is the problem)

Your print is lifting, this could be catching your hotend and forcing lost steps.

Also lost steps are not always the result hot drivers.... Drivers adjusted too LOW will have the same effect.

I also don't understand peoples reasons for cooling stepper motors... We run these things under their ratings specifically to keep them cool during our normal operation. If your motors are getting so hot that you feel you've needed cooling on them, it is likely you are over-driving them which would result in your drivers overheating and skipping.

1. Drivers adjusted too high or too low.
2. Prints are lifting off the bed.

Look into these two things.

I use heat sinks on my drivers and haven't needed a fan on them even during long prints. YMMV