Weird changes to past transactions after update

I don't expect any resolution here but merely need to vent my frustration at the mess that resulted after I updated my Quicken version today. Some transactions going back to 2014 which have not been touched in years suddenly had revisions to the Category. The revisions were a combination of coding symbols such as a rectangle. I have already started doing some global edit on the transactions to repair this but, honestly, what the heck?? If Quicken assures us that they will preserve the prior transactions when doing updates, then this should not be happening.
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