A Glitch in the Matrix

Challenger 17pdr tank (M.Bergman)

As I noted in earlier posts, I've started getting layer shifting in my Y axis.

I'm looking at various things to try to diagnose the fault. There doesn't seem to be anything physically obstructing the print head travel, and all the belts and pulleys seem to be clear. Everything moves cleanly under finger pressure.

My current hypothesis is that it's degradation of the SD card I use to print from, since all the models showing this behaviour have been printed from one particular card and a test cube I printed from another didn't suffer from it. I've reformatted the card, and I'm doing a test print from it right now, so in a couple of hours I'll see if that has had any effect. If not, I'll try printing the same file from a new card.