Oh, also:
- I saw the advice in Reddit - Dive into anything, which was basically “have you tried restarting the NAS” (yes I have, it didn’t fix it!)
- I saw Managed User Has No Access to Libraries, Admin Account Has No Problems - #7 by tommytg2, but the advice confused me (I work in website management, but I am far from a network specialist, so I struggle with the network detail bits!)