The first thing I would suggest is that you option while you select the boom mic track so you don’t have to go through the unlinking part. Holding down the option key while lassoing a group or selecting a single instance temporarily unlinks the audio and video and is a much safer way to work especially with sync sound. Now that you’re in the option key state of mind, lasso the lav audio on track 2 and option drag it up into track 1. This will make and move a copy of the track up to 1 and ensure it stays in sync.
Curious to see if this method causes it to crash.