I never had the Indexing issue but other users at my site do have it. Rebuilding the index seems to fix it but only temporarily. Issue I'm just seeing this morning, which I never had, but have had a number of end users report over the last few days, is that email messages received while I'm away and my computer is locked, do not display in Outlook after I unlock the computer. New messages will come in and display fine, but anything that came across while I was gone, do not display in Outlook. Messages are visible via OWA. I removed KB5008212, as I have seen in another thread that this KB introduced Outlook problems, although all I have read so far were issues related to the Search function. After the KB removal, I rebooted my machine, and then Outlook displayed all messages not visible before, but that may have just been due to my PC being rebooted, as I seem to be experiencing the same issue again, and the only way to fix it seems to be by restarting Outlook.
Exchange is on prem. Outlook access is remote, via VPN, in cached mode. Not sure that matters as this method of accessing Outlook has not changed in years, but this behavior in Outlook is no more than a week or so old.