If I had to guess, these users have %HOME% set to the one drive location, and cmdstanr is using it. Note that this is bad practice on cmdstanr’s part, %HOME% is not one of the standard environment variables on Windows so it can be set to more or less anything (or nothing at all!) unless R is stepping in and monkeypatching this.
In CmdStanPy we use os.path.expanduser which uses a combination of things instead of %HOME% on windows:
On Windows,
USERPROFILEwill be used if set, otherwise a combination ofHOMEPATHandHOMEDRIVEwill be used. An initial~useris handled by checking that the last directory component of the current user’s home directory matchesUSERNAME, and replacing it if so.
I haven’t seen issues with cmdstanpy and OneDrive yet, so I strongly suspect this difference is the reason