Originally Posted by CheshireBumpkin:
“As a workaround, you could try using ES File Explorer from the Play Store. It's a separate file management app that can be linked to OneDrive (and others) so that you can, for example, copy a directory from the device memory to your OneDrive space.”
I tried that, but for some reason it wouldn't connect to the OneDrive server. The error message was something like "Unable to connect to server - try again later" but the error never goes away, I tried repeatedly for 30 mins without success.
In the end, I copied all the folders and files I wanted to upload into a temp folder on my PC, which I was then able to drag and drop onto the OneDrive.