poss reasons for not working…
any audio fx/gain/automation differances across matching clips will stop the edits from disappearing, or, adjacent clips with matching tape and timecode but from differant masterclips!(ie, someone going back to digitise extensions to clips etc and just adding them on rather than replacing whole clips)
if safe to do so lassoo the whole sequence and keeping hitting backspace until the sequence disappears then undo one step and then try to remove mastch frames… this will lose all automation/gains etc but won’t sole the second poss reason.