I noticed the same thing. After a bit of searching I found: https://forums.thetvdb.com/viewtopic.php?f=7&t=24666&hilit=mythbusters
So they have decided to switch the seasons to use Year numbers instead to be in line with the listing on the Discovery website. Sonarr dumped my metadata for all my episodes because it is looking for s2013eXX or similar. I think they intend to keep them listed like this so not sure how this will be handled.