Alright, I changed now the position of the pulleys and omitted the tensioner on the carriage (I tensioned the belt by making slots instead of holes at the motor side and just pulled the motor while tightening the bolts. I doubt that this is good engineering but it seems to work). Therefore there is no more torque on the carriage and the belt is parallel to the steel rods. Now I'm going to run some long duration prints to see if the step loss has gone.
Also, I've read that the stepper motors perform better with 24V instead of 12V. Do you think that switching to 24V might solve my step loss problem? The heated bed is already 24V (controlled through a relay) and my new duet 2 board supports 24V as well. So guess I'd only have to change the hotend heaters and the fans and perhaps I'd need a more powerful 24v power supply but making the change would still be within a reasonable price range.
Also, I've read that the stepper motors perform better with 24V instead of 12V. Do you think that switching to 24V might solve my step loss problem? The heated bed is already 24V (controlled through a relay) and my new duet 2 board supports 24V as well. So guess I'd only have to change the hotend heaters and the fans and perhaps I'd need a more powerful 24v power supply but making the change would still be within a reasonable price range.