The workaround, pending the fix being deployed, is to stop Roon Core before copying files/folders into your Watched folder, and then restart Roon Core. See:
I get the impression that, since 1.3, adding new tracks to my library will frequently give rise to I/O failures.
In the past, to add new albums to my library, I’ve first downloaded or ripped CDs to a staging area, edited metadata if necessary, and then copied the album folders and contents over to my Watched Folder. This copy I have always done while Roon Core was running.
Since 1.3, I can almost guarantee that during the copy to the Watched Folder, at least one of the tracks will be marked as…