It’s as a result of the commercial skipping workflow being broken since 1.18.5.x.
Since that release, the commercials are no longer being cut - even if the EDL file is created. The work around is to disable the post-processing script, have MCEBuddy monitor locations for .TS files, and then run the conversion task as appropriate (either cutting out commercials or not, depending on where the recording is).
The challenge is that the .ts files are changed to .mkv as part of this - the only way to get Plex to pick back up the new file is to have it rescan. I’ve got it turned up to scan every 15 minutes, but it would be much more elegant to run it as the last step of MCEBuddy’s conversion.