I’m having this issue, too! Started after Dec. 20th for me (which is the very day I updated to Windows 11, version 24H2. I probably rode first and updated the computer later in the evening). I have a HP Pavilion gaming laptop with AMD RIZEN 7. The videos are 0 bytes on my computer and don’t show up at all on my phone, even though I do video capture through the button on the companion app while riding. Won some epic sprints today and quite gutted to not have the footage to relive it and show it off on Strava! 
P.S. My Zwift is updated to the most recent version: v 1.81.2