text boxes shifting in entire .indd document

I edit a large 120+ page monthly magazine. Last month, following an InDesign crash, I noted that ever single text box and image had shifted out of alignment - just half a centimetre off-centre.
I presumed that either the crash had caused it, or I had accidentally hit some secret keyboard shortcut I didn't know existed. I corrected it page-by-page, and hit publish. Annoying, but whatever.
I am now working on my next issue - and yesterday, following a crash, my workspace reset and I noted that every page object was out of alignment by that half a cm again. I manually corrected them all.
This morning, they are out of whack AGAIN, and the workspace has reset.
What am I missing? It's correctable, but incredibly time-consuming and frustrating.