Homing error X

Old belts can cause this issue.

This issue haunted my Mk4 and now my mk4s as well . It's a huge headache and disappointment. Fixes suggested here don't work. Fiddle and power cycle and pray is all that has worked thus far each time.

I’m a loyal customer that’s only ever had Prusa machines. After troubleshooting this endlessly, I have decided that after this printer, I will never get another Prusa. It just leaves a very bad taste in my mouth because I have to keep doing this. It will print flawlessly back to back to back and then this will happen and it can’t configure the x axis. Nothing changed, same print, same settings, no filament pieces anywhere, clean belts, lubricated bearings, blah blah blah. I’ll do all the steps, with zero improvements or fixes, get very annoyed, give up, then try again in a few days. Sometimes with success until it eventually will happen again because this is a routine I’ve grown accustomed to. Undoubtedly it will happen again, as it does so irregularly. I have had this issue for over a year now. I’m just a hobbyist, but if I relied on this machine for a business, it would’ve been in the dump long ago.

My MK4S was having a homing error, and the issue was it had been set to a MK3.9 in the settings somehow. So double check the printer type is correct.
I have had this for over a year, and I'm sure I didn't change that myself. I didn't do a firmware update before it failed homing, and none of my other settings were changed. So there may be a bug that causes the printer type to change on its own.

I am having a problem with calibration in the XY direction.Starting from powered-off state, I turn on the printer, and it tells me I need to complete a "Calibration & Tests" before I do any prints (this is expected due to prior calibration fails). I acknowledge and then go to Control --> Calibration & Tests --> 2 XY Axis Test. It does a Z-axis calibration, which seems to be successful. It then tries (and eventually fails) the X-axis calibration. In the X-axis calibration, it first repeatedly bumps the print head against the left side of its range (around 0mm X). Then it begins to move the head a bit to the right (a few cm from the left side of its range). Then it move the print head all the way to the right end of its range, and the displayed X-value increases to around 212mm, but then it suddenly changes back to near-zero as the print head is on the right. So, then the head is on the right side of its X range, but the X-value is reading close to 0mm. It proceeds to bump the head against the right-hand side for a while, then apparently decides that it has failed the X calibration test. It then conducts and passes the Y calibration test.What is going on? Initially the system displays a reasonably large and positive X-value as it moves the head to the right. But, then it just abruptly changes to near-zero. So, the head is all the way to the right - repeatedly bumping against the right-hand side of its range - and the display shows an X-value close to zero - as if the head were on the other side. What causes this? The printer is almost new. I purchased it a few weeks ago, but have not been using it until the day before yesterday. That is, I took it out of the box and set it up Saturday. The calibration went fine then. Over Saturday and Sunday I did several prints (maybe 4 or 5). Then, Sunday night, it produced an error as it prepared for another print, so I power-cycled and did this calibration test. There does not appear to be any debris on the belt or rail, and the belt tension seems fine. Today is Monday.I recorded a video that shows this entire test - from the power-on until the test reports a fail. I will post it here if there is a way to do so.