Both OneDrive Personal and OneDrive for Business offer handy ways to control how you sync files between your devices and the cloud storage.
What was the issue

One of the options allows users to limit the bandwidth used by OneDrive sync so that enough bandwidth remains free to the user. In both OneDrive Personal and OneDrive for Business this is in “Advanced Settings”:
Click on the cog > Select “Settings” > Scroll down in “Sync and backup” > Expand “Advanced Settings” > Turn “on/off” the option “Limit upload rate”. You can also expand the option to configure how much bandwidth will be allowed when the limit is enforced.

The problem is that, as it is evident in the screenshot above, limiting the bandwidth means that concurrently uploading a large number of large files will take forever to complete. Unfortunately, the UI does not offer a way to limit the number of files that are being uploaded at the same time.
What was the solution
It turns out that there is a configuration file in the OneDrive settings folder in AppData. This file is human readable and editable. Navigate to either:
%UserProfile%\AppData\Local\Microsoft\OneDrive\settings\Business
or
%UserProfile%\AppData\Local\Microsoft\OneDrive\settings\Personal
depending on what you’re working with. The file you’re looking for is
ClientPolicy.ini
and the setting you must change is the “NumberOfConcurrentStorageRequests”

This is typically set to “6”, so feel free to change to whatever works for you. One thing that is maybe interesting is that although I have set it down to “2”, OneDrive insists on uploading 3 files at the time. In any case, limiting the number of concurrently uploaded files means that the aforementioned limited bandwidth will now be spread over fewer files meaning that individual files will upload a lot more quickly and with, possibly, fewer hiccups.
Update [doesn’t work]
Turns out that, even though the aforementioned hack works, it only works for a few minutes; or until OneDrive decides to overwrite the file with a version it likes better. That means that, for some time, OneDrive will indeed obey the setting you manually enter, then overwrite it, then start sending much larger batches again. In fact, although it now has overwritten my “2” value with “6”, it is currently uploading 8 files concurrently. This is such a mess.
I tried to remove “write” permissions on the file, but OneDrive ignores that as well. I have now removed “write” permissions on the entire folder, but I don’t thing that that change will stick either.