Definitely strange – our apologies for the inconvenience.
It looks like you’ve already run through some troubleshooting steps but I just want to post a set of steps in full before we proceed any further. Ideally can you run through these (or confirm the outcome if you have already tried this):
- Please ensure you have the latest versions of The Events Calendar and Events Calendar PRO
- Deactivate all other plugins
- Switch to a default, unmodified theme such as Twenty Twelve
- Flush the permalinks (just visit Settings → Permalinks to do this – you need change nothing)
- Create a new recurring event as a test: are the permalinks formed as expected?
Hopefully we can get to the bottom of this 🙂