Puzzling.
The closest thing to a similar issue I’ve seen turned out to be a conflict (with Series Engine, I think the plugin was called, though that won’t necessarily be the case here).
With that in mind, would it be possible to:
- Double check that you are using the latest versions of The Events Calendar/Events Calendar PRO
- Deactivate all other plugins
- Switch to a default and unmodified theme
- At this point, there are a few things to test out:
- Do the events you already know to be affected still exhibit the same problem?
- If you once again try editing them, are you now able to correct them?
- At this point try creating a completely new set of recurring events … are they immune from this problem or do they suffer the same fate?
- If we get some positive results such as successfully creating a new chain of events without this problem, or being able to correct the existing events, start reactivating everything one at a time
- Check at each stage to see if your theme/a particular plugin causes the issue to recur
Is that possible here?