Solved
Gavin... which I am sure you were going to say,
...it is best to remove files from OneDrive and store them locally and not to use One Drive as a 'drive' for data in a project... Although it can be done, it won't work when needed most... but only in a pinch
…. weren't you?
No, that is not what I was saying at all. I didn't even mention OneDrive, but rather mentioned Dropbox. In fact, what I discovered (remembered actually) is that my selective sync DB folders are stored in a C: users path, so when I store them there, I get the benefits of speed of local drive plus automatic backups. I haven't tried it yet with smartsync, which may have the issue you described, but may not if I'm working in internet speeds of up to 1Mbit/s, which I realize I'm lucky to have, but some won't, and then I get the benefit of not taking up local drive space.