I have the exact same issue. Never seen it before.
I created a series of multicam sequences using two DSLR Quicktime .mov clips and a standalone .WAV file from a Zoom H4N. Done this setup thousands of times before with no issue.
For some reason, using Premiere 2015.0.1 it now refuses to play anytime I try to playback one of these multicam clips. I can still open and playback the individual Quicktime clips in the Source playback window with no issues but the multicam clips refuse to play.
Pretty frustrating. I’ll post a bug report to Adobe and hopefully they will get a fix out soon.