I recommend not scanning using the search drives button, or search folder, unless you know exactly how the BFD data in it is structured. BFD seems to choke when it runs into some situations where there are duplicate objects in the path. So, for instance, if you’re scanning a drive that has your installed BFD content, but it also has a directory with the downloaded data, that’s a duplicate, and a problem.
Also, even when the data is organized and well structured, there can be some scalability issues where it hangs. I’ve seen this for directories where there are a lot of grooves, so it’s not entirely related to kit pieces and audio content.
At least initially, it’s better to point it to each individual expansion, one at a time, and scan them until they’re all in.