I contacted the support and they said one motor was failing on my 2 weeks old machine, did the replacement, first few prints worked fine-ish then now reappeared. Checked belt tension they are perfect.

The layer shifts were constant before into a specific direction and after change it went into the other direction....

Another popular cause is that a pulley which is not properly secured on the motor shaft. It's worth checking the two grub screws on either side. Do you have a factory-assembled printer or a kit?

Assuming that the shift occurs in a 45° direction, which corresponds to movement of one motor only, the displacement direction you observe will tell you which of the two drive trains has a problem.

Also, collisions of the nozzle with the printed object may cause displacements. Do you notice any lifting corners where the print detaches from the bed, or excess filament (blobs) on the top layers?

I contacted the support and they said one motor was failing on my 2 weeks old machine, did the replacement, first few prints worked fine-ish then now reappeared. Checked belt tension they are perfect.

Was never far off "correct" and didn't notice any change in print quality. 

Same here. I do re-calibration every now and then (with auto belt tuner and also that with accelerometer), but so far i didn't see any print degradation or improvement after re-calibration.

Anyway, prusament is just too nice to actually use. My samples (from mini+ kit and core one kit) are still sealed in their bags. 🤪

Back on topic, tensioned my core one on first build, again when the belt tuning strobe firmware was released, and recently before redoing the accelerometer tuning with the recent firmware. Was never far off "correct" and didn't notice any change in print quality.  

If we go forward: when i bought MMU3: a nice thing would be to enclose 5 samples. Again, small spools would do...

it's like... say you buy a car at your dealers but you don't get a single liter (or gallon) of gasoline inside, so first thing you must do is to walk to a petrol station and buy some to be able to drive home...😭

Except then people would complain they're being forced to buy filament of the wrong kind or

It's not about right or wrong filament, it's that you assemble the printer and then you can't do anything with it until you buy some filaments... not even test it. And, sith 10+ kilos of printer one roll of filament won't increase postage... 

as said: we get a feeling that we're a second class buyers, just because we like to assemble and know how it's made...