This exact problem happened with an optic in my lab in graduate school. For two years the senior grad student and postdoc blamed each other over the entire apparatus becoming misaligned every couple of days. (It was a really toxic environment.) Eventually, they both left, I was the only one there, and it still became misaligned. In one day I tracked it down to a prism from Thorlabs whose glue had gone bad positioned at the very beginning of the laser line- it was sliding in its mount.

I wish I had pushed more strongly about it. We spent probably a full person-day of work every week on that.