Does that refer to the temporary workaround mentioned in Release: 2.0.3.12 (canary) 2018-10-23 pointing to Path on server needs / at beginning when configurations are edited #3460? If not, could you clarify it please?
Microsoft Graph error responses and resource types says
400 Bad Request Cannot process the request because it is malformed or incorrect.
Addressing resources in a drive on OneDrive explains its format. I’m not sure if a double slash is helping any, and what’s the # for (and is that character allowed)? I’m not a OneDrive expert, and can’t help more in depth.