It can happen if you ran an update in between and the update corrected actual errors on the return.
and ex marks the spot where those rocks and anvils hit me.
I think this is why users pushed to get LOCK the return. https://proconnect.intuit.com/community/help-articles/help/new-for-tax-year-2017-proseries-return-lo...
Then you'll never know if something changed and your return is wrong until you get the IRS notice.
Sooo many times I open a client file and get that "things have changed" message, only to find that NOTHING changed, everything is still the same.