After months of successful printing, I suddenly developed an issue with x-axis layer shifts while trying to print the same "Hell's Bell" that I'd done on the Neptune 3 and 4 Max printers.
This video covers days and days of frustration as I attempted 6 bells and 5 test cubes.
I had the belt as tight as the adjustment screw would allow. I ended up disassembling the whole x rail to clean it. What you don't see is the fitting of a new x-belt which failed when the brass crimped end came free during a print, which made me revert back to the original belt (I'll fix the new belt with a fresh brass clamp later).
After doubting the filament, Cura, the motor and the printer gods, I eventually used wooden dowel rods to allow me to add extra tension to the old belt.
The lesson from this is: Never give up! :-)