I don’t have that particular series and don’t think it was due to a series with duplicate TVDB seasons. I went through all my series’ links to TVDB and checked.
I removed a bunch of series that were unmonitored and didn’t have any local data, also fixed one particular series (Dragon Ball Super) that wasn’t finding local files I DID have. Dragon Ball Super got stuck where there was a file with an encoded character in the filename (slash with a couple numbers), and also this series had local folders of both the Season [00] and Season [0] formats of the same seasons with episodes in both, maybe that was the issue? Once I cleared those up and upgraded, I could get in, and added back the unmonitored shows I previously removed without issue.
In any case, now successfully on v4.