Altho I don't know what is happening with my Mac programs, with my most recent upgrade (almost a year ago), I am still somewhat closer to prehistoric than most. My upgrade is working smoother than the previous upgrade, but until recently, every time I opened a doc from the old format, i would have to struggle a long to figure out why/what/where the doc was not working properly. I finally figured out how to upgrade each doc as i discovered a problem. I had to prompt the upgrade and usually did not prompt unless I found a problem (Spread sheet only). Suddenly, if i go back in time, A message comes up on the screen that TELLS me to upgrade.
I really have no idea why the sudden change, but I go with the flow.