Multicam issues in source monitor

I'm having an issue with my multicams! 

Working on premiere productions, footage from an A7sii, proxies in QuickTime toggled constantly. 

When I play my multicam as a clip in source monitor, it starts doing the beach ball as soon as I try to mark in and out points, or even play / pause! 

If I place the multicam clip on a timeline, and make cuts and edit the multicam there it's totally fine. Any thoughts of what it could be?