Switching Angles on Locked Tracks
You cannot switch or cut a multiclip item in the Timeline if it is on a locked track. For
example, suppose you have a multiclip whose video clip item is placed on track V1. If
you choose View > Multiclip Active Tracks > Video and then lock track V1, you cannot
switch or cut to other video angles of that multiclip.
Furthermore, if you choose View > Multiclip Active Tracks > Video + Audio and then
lock any video or audio track in the Timeline that contains a multiclip item, you cannot
switch or cut that multiclip item.