Why does the "undo" function keep getting greyed-out in MS Word?

Question

I'm using the MS office 365 proplus. When I'm using Word, sometimes the undo button is greyed out, and I can't undo with ctrl+z, it just doesn't do anything, as if there's nothing to undo even though I typed a lot of stuff right before.

I corrected this problem before manually by editing the level of undo in word in the registry entry, which somehow became "0" even though I never changed it. But now it is happening again.

It would be extremely frustrating to modify the registry entry every now and then (if that's even the problem). So I would like to know what's causing the undo button to lose function in the first place.

Thanks for your help!

Answer 1

There are certain actions, such as locking/unlocking forms, that clear the Undo stack. I believe I've seen this behavior with content controls as well.