Acccessing files on SharePoint

I am finding DO and SharePoint inconsistent. Sometimes I can see files on SP when using WindowsExplorer but cannot see them using DO. Conversely I can sometimes see files on SP with DO, which WE cannot see. I think the difference might be happening if I upload files to SP from C drive using SP. How can I get DO to see those files on SP?
I can readily add or delete files on SP with DO.

This sounds like a SharePoint issue if it affects both Opus and Explorer in similar ways.

SharePoint isn't something we know much about, so it may be worth finding a forum with SharePoint experts to see if they have run into similar problems and have suggestions on solving them.