Soundtrack Pro will no longer open

I have Final Cut Studio installed on my newer Mac, and have specifically not upgraded to High Sierra so I can still use all the apps. FCP7 still works good, but out of nowhere Soundtrack Pro is not opening anymore. I didn't do anything new to my computer, and I literally opened it yesterday and it worked fine. It gives me the message "Soundtrack Pro cannot be opened because of a problem". I've tried any potential fixes I've read on past posts including completely uninstalling and reinstalling Final Cut Studio, as well as finding the hidden installer folder and installed "PSTSharedA.pkg" and "ProAppsMetadataSupport.pkg" - and still it doesn't work. Really not sure where to go from here so any advice would be appreciated.