Unity3d Mac project freezes when importing ogg/mv4 files on external hard disk

Updated to Catalina on Mac Pro, since then if I try to open a project on an external hard disk it will freeze when it encounters mv4 or ogg files. The import will stop on the first file of this type that it encounters. Have to kill the Unity process, and sometimes even after the process is force quit the import dialog will remain up. This implies that Unity started a separate importer thread, possibly an external helper app, or something like that. Just guessing.

After updating to Catalina any time I open an application the OS goes through a "verification" step the first time that takes a long time. I am wondering if the process handling the import is something like this. Catalina won't let it run until it is verified, and because it's a helper app that Unity uses, it never gets verified. Unity waits forever for the import process to complete.