I understood you and I agree, it makes no sense why this would happen because everything seems to indicate it's the same file - same time stamp, same information (at least saved in the actual questions), no other files, same SaveAs location. No flash drives/cloud drives are in use, so can't be those.
You might be on to something with the update, as the update is what caused the issue in the first place. Though I can't test that anymore since this last time I opened the file directly seemed to "stick" and updated the Continue tax return to have the correct numbers now. Took a couple of times with the different opening methods, which REALLY doesn't make any sense as no other updates have been installed.
