@taraba I do not have “Convert video while recording” set to Transcode. It is set to off.
If Plex truly does not support back-to-back recording on one tuner natively, then the only thing I can think of is that this server also has (had?) MythTV running on it. Could a file required by MythTV benefit Plex to be able to do this?
I also was using a Nvidia GT 730 to hardware transcode which I did not find supported in any docs. Sometimes you just have to try it even if there are info saying otherwise or not mentioned at all.