Random application of autocorrect

On Office 365 Word Version 2201, I have found that autocorrect/autofill has modified items that I am not currently editing. This includes some that I have setup that take a two-letter entry to complete the full word.  Not mine, but an example would be typing "ac" to get "AutoCorrect". Others I setup and used for years include making sure items are the correct case.  

In both cases I have noticed this, Track Changes was on.  I expect these things to happen when I am entering or editing words o, but not on other parts of the document I haven't edited.  There seems to be a trigger that suddenly runs all of them, and the rule above will change every "AC" combination in the document to "AutoCorrect".  If I see it and catch it, ctrl-z undoes it.

This is how I usually work with documents, so something must have changed recently. Any thoughts?