I am not sure if anyone else uses this feature on their site but we recently reported to Microsoft that, with the May 2017 CU, Reusable Content breaks if you have sub folders in your reusable content list. It was confirmed by Microsoft that this is the case with all CUs past the May 2017 CU, up until September.
If you try to access any content items that are stored within sub folders from the top level, you cannot navigate down.
This is supposed to be fixed in the November 2017 CU, so we are anxiously awaiting this. Hopefully the other issue from October, which breaks site creation, also gets fixed.