The problem is acute for both Catalina and Mojave.
I can not drag and drop a bunch of audio assets into an instrument. Rebooting helps, but only until I try to drag and drop the assets again. Here is the video of what I am talking. Many friends of mine face such an issue.
This is a known issue, and has been fixed in FMOD Studio version 2.00.08. It was introduced in a recent version of macOS, and makes it impossible to drag browser items as soon as you select multiple items in any browser.
Incidentally, you don’t actually have to reboot your machine to make it possible to drag individual assets again. Just exit and relaunch FMOD Studio.