We just select one or more photos from the contact sheet, rt click, and go. Copy Wave files is checked as is Clear "move photos" and Clear Overwrite. We have "Copy to this folder....") And open destination as a contact sheet.
Happens to both Canon RAW files and jpegs that PM extracts from them.
Again, this only seems to happen when copying TO the QNAP NAS. When I copy from the NAS back to that original disk, it works fine.
I should also mention that the NAS is mounted as a Disconnected Network Drive so that Lightroom can read catalogs from it. (I know, I know.... Shouldn't, but have been doing it for as long as Lightroom's been around.) And others have had this problem that are not doing things that way, so i don't think that's contributing to the issue.