A Microsoft file hosting and synchronization service.
Here is the statement from the Microsoft OneDrive product group (Redmond USA) about the OneDrive Personal problem:
***This is related to a backend migration we are doing and unfortunately, we don’t fully support syncing shared folders in the case where one user has migrated and the other has not. We’re doing everything possible to accelerate things so that it can be resolved as soon as possible for users of the feature. When the accounts are migrated, there is automated logic that makes them go back to a syncing folder within several days.***I have heard, that shared Folder issue is gone.
The best thing is: WAIT and do nothing