my write to USB completes, but activity remains for a minute or so
I’m afraid it’s not really a new issue. Graphical front-ends / DE shells for files operations sometimes show « everything’s fine and done » although the system is still actually writing onto removable-media or archive.
Hence @fossfreedom’s suggestions about caching. I guess the graphical front-end or shell for file operation is sync’ed with the « first level » operation and not with the « caching » operation. For light / small files it’s not a problem, for bigger ones the lag between those two levels of file operation becomes visible ( big question mark here → ? )
many problems using rsync, USB drives file copying to local or remote.
Meaningless to say but source and destination for file operations should always be accessible to each other during the whole time of operations. I don’t know what kind of « remote » you refer to, but ensure everything’s always there / on / connected / online, both sides.
I cant see any settings for admin permissions anywhere
Permissions and rights issues may also lead to I/O errors in some case.
It’s also related to the filesystems in use in your setup, betweens source and destinations.
Maybe some adjustments needed regarding who’s doing what, owners, writing rights ?