I have 4 network folders set up in folder monitor to be watched. Each is set to scan after start-up completes. On previous builds the media library would remain available when the folder process scan took place and then the library would be updated and new files would be available. On the current preview (1.99.27.21136, March 9 2025) the library will become empty while the folder process runs. Additionally, the folder scan process will sometimes fail (timeout) and not complete rendering the library empty, or only partially populated.
I see that the beta changelog has several updates to the library scan process, perhaps this is a known / fixed issue, if so please ignore.