GarageBand 10.1.1 Removed MainStage Instruments

After updating to GarageBand 10.1.1, all the instruments I've downloaded from MainStage 3 have disappeared from the instrument library. They still seem to be in /Library/Application Support/GarageBand/Instrument Library/Sampler/Sampler Instruments, but they're not showing up in the list. Any projects with the instruments, however, play perfectly with them. I'm not talking about Jam Packs here; they're still right there in the "Legacy" category. I'm talking about things like the expanded orchestral strings, world music, etc. How can I get these back? [Topic on the Apple website.](https://discussions.apple.com/thread/7526588)