A little more on the system:
big fat fast i9 CPU, RTX 2080 Ti GPU
Lots of RAM.

Logging in to the system on an Active Directory domain user that's in the Local Administrators group.

C: is an SSD, and N: is a pair of spinning rust disks in NTFS striped Dynamic Disk configuration. Boinc is installed on C:, but its data directory is configured to be on N:, in "N:\BOINC Data". Anyone telling me not to have spaces in the directory name will be ignored because the default location has spaces in its name.

Anyway, it's fine for a while after I delete gui_rpc_auth.cfg from "N:\BOINC Data", but suddenly, in the middle of the day (er, while I'm not there, duh), it will lose track of the password, and pop a dialog box reporting that it has an invalid GUI RPC password. If I shut everything down (including killing 36 tasks via Task Manager (er, yes, it's a *fat* CPU)), and delete gui_rpc_auth.cfg, it creates a new one, and works fine for a few days. BOINC Manager is the latest one available.

Any hints on how to fix this? (Is it a permissions problem on the data directory?)