Groove support forums user AdamK might have found the reason why Groove sometimes stops synchronizing files in shared folders – a hidden “Temporary” setting for files on your hard drive. When Groove sees this setting, it decides to skip the file, but the error message displayed does not make it clear why the file is being skipped.
Right now, Adam doesn’t know what causes the files to be marked Temporary, but he’s found a commercial utility that will reset his files, and more. Snag is, it costs $24.99, which you might not want to pay- especially if you’re planning on migrating away from Groove anyhow.
Licensed Bambuco users can email me for a script that will turn off this setting for you automatically, free of charge.