Staging Gone

[DStaal]

Putting this here because I have a modded (39 mods - most of USI, along with Mechjeb, AVC, etc.) install, but this is specific to a particular save - other saves on same install work fine.  (Or appear to - I don't have any other saves with more than one flight.)

I'm about halfway through my first playthrough, a science-mode run under CTT, and staging is suddenly gone.  As in: I can set up stages in VAB, but on the launchpad they don't exist.  Nothing along the side at all, hitting the spacebar may or may not activate a particular stage at random (almost always not, but occasionally one stage will fire - not always the next on the list either.  I've had it activate the top stage without activating anything below it.  Also, sometimes it will sound like something's activated (the 'engine start' sound), but nothing actually does), and in general launching/flying is completely borked.  Mechjeb autostaging appears to mostly work - if I can get the launch to start in the first place.  (But I've had Mechjeb stall out when it should be activating the next stage too.)

I'm on a Mac, with KSP from GOG.com.

Any ideas?  Obvious solution is to start over, but I'd like to keep my progress if possible.  (And I fear that unless I know what happened, it could happen again at some point.)

[Spilled Vial]

I'm not sure specifically what is happen, but I know USI tends to cause problems with my GUI. If you have the BioMass mod, that also causes massive GUI glitches.