Regular Y-shift for each layer starting after the first few layers

My printer was printing ok for weeks, but now suddenly it started to shift each layer a little bit more to the back (Y-axis) after the first few layers

I already checked for loose belts or screws, couldn’t find any.
Interestingly this does not happen for all models: When I print a simple tower with an edge length of 6mm, it does not happen.
Any ideas what this could be?

I think I found the solution by myself: the screws of the T-rod nut were loose, see this video around 0:20

Unfortunately this was not the solution. Had some working not so complex prints, but now another one failed.

For layer shifts check:

Belt Tension: Ensure your belts are neither too loose nor too tight. Loose belts can cause slippage, leading to layer shifts. But also overly tight belts can strain the motor and make it difficult for the axis to move smoothly. Aim for a balance where the belts are taut but still have a slight give.

Obstructions: Check that nothing obstructs the movement of the printer’s axis. Dust, debris, or even tangled cables can impede smooth motion. Regularly inspect and clean your printer to ensure all paths are clear, and the axes can move freely.

Lower Acceleration: This could be the issue here if just certain models fail, maybe they are sliced with high acceleration values. High acceleration settings can cause the motors to skip steps, resulting in layer shifts.

Stepper Motor Issues: Problems can arise from too low stepper motor currents, broken wires, or faulty drivers. Ensure that the motor current settings are adequate for your specific motors if all other steps didn’t help. Check the wiring for any breaks or loose connections, and if the problem persists, it could also be the stepper drivers (the main board) this would be the worst case. The motors themselves are usually robust and less likely to be the root cause.