I was not able to reproduce the bug. Maybe you need to remove the minVideoBW for the localStream you want to record and try again?
Bandwith may not be calculated correct at the beginning of the stream.
“Would providing only audio to a subscriber and no video to subscriber prevent any recording degradation of speaker’s video?”
Maybe. Its hard for me to simulate low bandwith. For testing you could publish the stream (you want to record) to two independend rooms. One with other subscribers one empty. Then start recording on both and compair the results.