Yes...Same issue here. I'm using the Flatpak version of OBS.
After upgrading to OBS 30.1, "Source Record" plugin still works, except it won't stop recording when I clicked "Stop Recording..." on OBS main control dock, thus showing the "Stopping recording..." message. Until I exit OBS completely, at which point OBS would prompt me with a message indicating some recording is still ongoing and asked if I really wanted to "Quit". Only after I exited OBS would the "Source Record" plugin stopped recording. I confirmed that after checking the corresponding recorded videos' time-stamp and length.
I can also confirm that by downgrading OBS to 30.0.2 would restore the stop recording functionality for "Source Record" plugin.
I like the added feature (not to mention fixes) in OBS 30.1 such as VAAPI-AV1 support, but I also need to retain the ability to record a source separately. But if I have to choose, I would go back to OBS 30.0.2.
Lastly, many thanks to Exeldro for this amazing plugin (and many others). I've been a fan for several years now and can't say enough how his plugins have streamlined my streaming and recording sessions! Thanks again.