A Microsoft file hosting and synchronization service.
Another of our accounts is now back working, so they are obviously working through a phased release. In that case, it needed a couple of steps to get it working correctly as I had deleted the links on OneDrive on the PC but they were there on OneDrive on the Web, so OneDrive for Windows was stuck trying to synchronise the changes around them. In this case, deleting the links to the shared folders both on My Files on the Web and on the PC, and then recreating them from the Web (or from the Android App) then worked correctly, and they are now synchronising correctly.