This is Docker on Debian, and Linux doesn’t have a hidden flag…? Is the NAS a Windows box with an SMB mount from the Debian box? Or something else and things look hidden from Windows clients looking at the NAS? Even so, Syncthing on Linux (Docker) doesn’t (and can’t) set a hidden flag, so not sure where it would come from. Perhaps some default ACL on the NAS that is getting inherited? Some magic the NAS does to set a “hidden” flag on dotfiles that doesn’t get cleared on rename? 