REALLY odd "muting" of multiple audio tracks -- no rational explanation? Help!

Hello all!
 
I'm encountering a very odd, very irritating problem on a project that I'm currently mixing.
 
At about a minute into the song, half the tracks suddenly have no audio whatsoever. This happens with several of the tracks simultaneously (8 or so drum tracks, bass) and three others slightly afterwards (tambourine, guitar and room mic). All of these tracks are currently routed to buses, but not with each other. The audio goes silent, at the exact same place each playback, and then comes back about fifteen seconds later, again always at the same place.

Compounding the mystery, the takes themselves are still visible on their individual tracks. This is definitely not some weird muting that I've somehow accidentally automated--the signal just disappears on the channel, even while the audio clip is still visible. I've checked take lanes--there are just the individual clips. I've turned off all effects--still no help. I've soloed the channels in question--they still "go dark" at the same place.
 
Anyone have any insight into what might have happened, and what I might do to make it right? Anyone have any ideas at all?

I can possibly post a video of the behavior if it would be helpful. I also have a (much older) version of the project with the basic tracks (but no vocal overdubs, mix, etc) that isn't exhibiting the behavior, so that's my backup plan, but with the complexity of the mix that I have so far, I'm hoping to avoid that if possible.
 
Thanks for any insight you all might have for me!