anyone ever experience SB just deleting a bunch of data. All my Assemblies no longer contain members. System Information even shows nothing

Did you not turn on Advanced BOM in the sandbox?

I think that mightve been the case. We have provisioners prepping the environment for some demos.

Yes, if that's what you see now.

System Information showing nothing is standard. It's annoying, but they don't bring any of that over when the Sandbox refreshes. It should record new changes you make in Sandbox though.