Interesting bug reported on Discord the other day: on Windows, if the font files are in a OneDrive folder, OneDrive will bump the modification time when syncing a changed file , causing Fontra to receive another "file changed" event, making it think the file was changed externally, although it hasn't really, making it reload the data associated with the file.

Fixed in the latest release: https://github.com/fontra/fontra-pak/releases