Sync Selection to Monitoring Angle is greyed out

I have a multicam clip in which the option Sync Selection to Monitoring Angle is greyed out no matter what I do. I have other multicam clips in the same library for which that option works, and I just created a new multicam clip in the same library for which the option works. Unlike my other libraries, this library has been giving me a lot of beachballs. Might there be something wrong with the multicam clip that's also causing all the beachballing?