OK I did end up solving this and thought some people might want to know the solution. It was related to something that was packaged with I think an iTunes installer.
The problem was with something called MobileDevice.framework. It basically can break a bunch of stuff if you get the wrong version installed. What I did was go on my laptop where I had a previous version and copied that file. I booted up with Cmd-R, disabled SIPS and went back and replaced my existing version of MobileDevice.framework with the old one. Now everything that had been broken works again.
Hi! Literally created an account on this forum and resurrected this thread three months later to thank you for sharing this. I've been grappling with (seemingly) a near identical problem this last week that left me thoroughly frustrated. Like you, I'm on Sierra - incidentally, I'm also a Cubase user! Though I also replicated the problem in anything I had available - OBS, Reaper, etc. The problem affected multiple plugin manufacterers, but not all - and in some cases, not even all of the plugins from one manufacturer.
It affected both my desktop Mac Pro, and my MacBook Pro laptop, which baffled me, but which indicated that it had to have been something that happened to both machines when connected online - indeed, when I would roll back to a working version of my system drive, the problem would only recur once connected online.
After a bit of investigating, I too tracked the problem down to something to do with the MobileDevice.framework folder under System (in fact, it was only doing so that even gave me the correct combination of words to Google and eventually stumble across this thread). The folder contained files with a Date Modified time that exactly matched, to the minute, the start of the problem, and I was able to voluntarily recreate the problem myself just by copying this folder onto a working version of the drive.
Anyway, excuse the long ramble, it's cathartic to find someone who found the same issue after a week of scratching my head.
Three months on, have you had any trouble since, and did you take any steps to prevent these files from going rogue again and updating erroneously again? I obviously understand the basic concept of just copying across a working version of this folder, but I suppose my question is whether this folder will see fit to just cause this problem again if left to its own devices?
