Extreme lag when editing captions

WTF is going on with the captions editing?  I used auto transcribe to create captions which worked fine but now I need to fine tune the placement of the captions, correct spelling and adjust the timing.  When I double click to edit a particular caption it works ok but then when I go to move on to another caption or play the timeline there is an extreme lag.  Some times over a minute long before I can do anything.  Sometimes I get the spinning wheel of death for a while.  Also when I try to save as I go it takes forever for it to save even when I have only made a couple of adjustments.  For reference I'm using a Mac Studio with M1 Ultra chip, 128g Ram and 48 core GPU.  I've tried reducing quality to 1/4 and it does not help at all.  Normally I edit with full quality without any lag issues.  This is with 4k 24p H264 footage.  Right now this is completely unusable.