Cross Dissolve transitions disappeared between editing sessions.

Using the latest version (20.3.2), but this problem has been happening occasionally since at least version 19 and I have experienced it in Davinci Resolve on Windows and Linux (Mint 22.3 Cinnamon).

Sometimes I save and close a project that has many small clips with a lot of simple transitions (mostly cross dissolve or Dip to Colour) and when I reopen it, ALL of the transitions are gone - not just the ones I added in the most recently-saved session, but all of them going back to the start of the project.

This just happened today - no upgrades to the software; no changes to configuration, no installation of any new plugins or features; no changes at the OS level - just saved a project this morning that I have been working on for 2 days, went for lunch and when I came back and reloaded it, no transitions at all between any clips, all the way back to the start of the timeline.

I'm not ruling out human error - is there some key combination that I might be accidentally pressing that selects all transitions in the project (and thus makes the step of accidentally deleting them all much easier to commit)?