That’s not a new bug for me, I’ve been dealing with this one for a few years new, across multiple PCs and Thunderbird installations: some of my appointments disappear from Thunderbird calendar. Forcing a synchronization achieves nothing: the appointments are correctly available on google calendar and are missing from Thunderbird.
From time to time I need to unsubscribe from the google calendar, re-subscribe and for a few days everything is fine. Then appointments start to disappear again… rinse and repeat.
Now, I understand it’s impossible to point out what’s going with so little details, and in fact my question really is: what can I do on my side to identify the root cause of this? Are there error logs I can check or other clues that can help with that?