Layer Shifting/X Axis alignment Issue  

Layer Shifting/X Axis alignment Issue

Using an MKS3+ on this.

It took me a while to work out what my issue is and it boils down to the X axis, either the belt or the stepper motor. 

I had trouble, at first, with print head alignment and, at the time, thought it was a sensor issue. Basically I'd get a message about a forced Z axis recalibration. That was because the printhead would slide all the way to the right, then slide about halfway back instead of going all the way back. So, during the pre-print bed leveling, the head would never go back to 0 on the X axis. As I said, I thought it was a sensor issue, but I found out it was the belt. So I tightened it and it worked fine for a few prints. Then I started having trouble again.

I figured the belt was not as tight as it should be, so I opened up the back of the print head, took the X axis stepper off, cut off a notch on the belt and re-installed it, so it'd be tighter. I re-adjusted the screw that positions the X stepper motor, then re-attached the motor. (Which took a bit of effort because the belt was tighter now.) I recalibrated and things looked fine while I was printing my test squares (a 5x5 grid that covers most of the print bed). I didn't see any issues with the X axis or control. So I started a print and left it. Then I checked on it with OctoPrint and my webcam a couple hours later and had a nice start than a bowl of spaghetti. I looked at the webcam video. Here's a screenshot after it messed up:

I stopped it and the next print was okay. Then, after that, I got this on a similar part:

And then, a little later:

Basically, the print head was not returning to 0 on the X Axis, it was only going halfway back. Later screenshots indicate that at some point it did start returning to 0 on the X Axis.

I found this page about the belts on the MKS3 and checked my belt status. It says the belt tightness should be between 260 and 290. I'm not clear if that's for both X and Y axis, or just one of them. So here's a shot of the status:

It appears both my belts are too tight. I haven't had an problems with the Y axis, but that's not too far off. But, clearly, the X is off. I'm surprised I'm getting this issue with too tight a belt, since I would think a tight belt would keep it from slipping. Or is the belt so tight it might create a problem with the shaft on the motor?

Questions:

1) Is this so tight it's a serious issue? (I'm guessing it is.)
2) Could this be damaging the motor itself? Or could it be stretching the belt?
3) Could the tight belt be causing the problem with the printhead not returning all the way to the left, at X=0?
4) Is the Y axis belt an issue at 240 (since it's below 260?)

I like keeping some parts in stock, so, while looking over this, I've ordered replacement belts and steppers. For now, I'm going to readjust the X belt so I can get a number closer to the specified range. Any additional insight and advice on this is appreciated.