How to fix a Thunderbird Lightning CalDAV synchronization issue

Today I learned: How to fix a synchronization issue with Thunderbird Lightning (calendar and tasks).

What was the problem?

I upgraded my laptop to Fedora 38. That is the only remarkable thing I did. A day later or so I realized, that my tasks in Thunderbird were not synchronized anymore. The same Fedora upgrade on my workstation did not yield this issue, so I consider it a flake. However, as this has happended to me before under entirely different circumstances, I wanted to share my solution to the issue.

How I fixed it

My fix is very simple and kind of a sledgehammer method:

1. Stop Thunderbird and make sure it exited cleanly.
2. Navigate to $HOME/.thunderbird/$YOUR_PROFILE/calendar-data where $YOUR_PROFILE is the identifier of your current profile. It should be easy to figure out from the access and modification timestamps.
3. Move - or delete - the following three files: cache.sqlite cache.sqlite-wal deleted.sqlite.
4. Start Thunderbird and wait for Lightning to synchronize.

Wrapping up

This is neither an elegant solution nor do I understand the root cause of the issue. But it is a works-for-me kind of deal, and maybe it works for you too.