What you describe is partly an annoying bug that I’ve yet to find, and partly just the UI not being entirely sensible.
For the second case - the UI communicating poorly - what’s happening is the processing engine is probably updating metadata on items in a different day (most likely today), but it’s still showing that “updating metadata” bar even though nothing in that day you’re looking at is being updated. I need to fix that, because it’s misleading.
The annoying bug case is one where … well, if I knew how to describe it well I’d probably know enough to be able to find it and fix it But basically yes, sometimes it does appear that old data starts getting reprocessed when seemingly it shouldn’t. And also sometimes it gets reprocessed repeatedly, on a seemingly endless loop every few seconds, while you’re sitting there watching it. That’s the case that worries me the most, because it’s a waste of energy/battery.
If you see the unconfirmed count on an old day start high then gradually nudge down until it disappears (eg 3, 2, 1, gone), and it doesn’t get stuck repeating forever, then that could actually be a good thing (albeit one I’d like to see happen less). In those cases what might be happening is there’s some items in the timeline that weren’t confirmed at the time, and maybe did need confirmation at the time, but now that the processing engine and classifier models are having a fresh look at it, they’re concluding that they now have enough model data to be confident in their choices for those items, so they don’t need confirmation anymore.
It really depends what your life is like. If your life is one of familiar routines with little change, then yes, what needs or doesn’t need confirmation will stabilise and not change over time, with the classifier models becoming very stable and accurate.
But if you have a more complex life (in terms of places, modes of transport, common routes, new routes, etc), then the models will be constantly changing over time based on your new confirmations and corrections, and that will then change how those models perceive old data.
For example if for a month you walked from home to a particular Starbucks every day, the activity type model for that neighbourhood would learn the walking route and become confident in it, and it would learn the Starbucks model and become confident in it. No more asking for confirmation.
But then the next month you also start cycling to the Starbucks some days, you go there at different times, and you also stop in at a bakery next to the Starbucks before heading home. Now the activity types model for that neighbourhood is aware of both walking and cycling along that route, different times of day, and there’s also multiple competing places very close together, all adding up to reduced confidence in each classification.
Then with that more complex model data, if you browse back to a day in the previous month, that previously needed no confirmation because the models were simpler and more certain, now those unconfirmed items won’t look so certain to the classifiers anymore, and you’ll get asked to confirm them. Basically a month ago it could confidently say “you walked, and you went to Starbucks” but then with the new knowledge, and looking at that old data, it has to say “it looks more like walking than cycling, but the difference in this case isn’t significant enough for me to be highly confident. and it looks like Starbucks more than the bakery, but again, I can’t be as sure as I was at the time”.
A pretty common effect is to go back to old data, then get asked to confirm some stuff that you feel sure you must’ve confirmed at the time. But in reality you didn’t confirm those items at the time - the classifiers/models were confident enough in their auto assignments at the time, so didn’t bother you with asking. But now that the models know more about your life, they need to ask.
There’s a UX angle to this that I think is an open question: Whether the app should bother asking for confirmation for old data, or whether it should just leave it be. “The past is the past”, kind of thing. My personal preference is to have it ask, because I’d rather get it all right and not leave any little mistakes in my old timeline data. But I recognise that a lot of the time it’s annoying and tedious. So yeah, still an open question.