I have a similar CT'c which was the first gen made of all metal .I swapped out the extruders for MK10's and I swapped out the controller for an Azteeg X3 Pro and a VikiII LCD from Panucatt devices. Now fully open source.

However I never had an issue with shifts on mine even when stock.

Also forgot to mention that I included the picture of the miniatures because that's the only print without the shifts.

The main issue is layer shifts (see pictures). It seems to happen mostly during the infill phase, but only on prints with a larger surface. I suspect it is some sort of mechanical issue because it happens every time the carriage passes a certain critical point along the y-axis. There seems to be a connection with strange clicking sounds coming from the machine, but I do not have sufficient observations to be entirely sure of this. When trying to manually move the carriage along the y-axis there is some sort of resistance that seems to coincide with the critical point I mentioned before. I can move it all the way along the x-axis without any change in resistance but along the y-axis it is like a sinus function: it gets more and more difficult until the critical point, and after that it gets easier.

So far I have tried the following. I checked everything I could reach without taking things apart and tightened anything that was loose. During this check I did notice what looks like some sort of damage on one of the belts (see picture). I doubt it is connected to the issue, but it is concerning and I really do not want to be the person who doesn’t include information that turns out to be vital. I lowered both the printing and the travelling speed several times, down to the utterly absurd 10 mm/s. I tried changing the temperature a bit, heating the bed, not heating the bed and using a different brand of PLA. None of these helped at all. Does anyone happen to have any ideas or possible solutions? Thanks for reading!