I recently ran into an issue after updating MIM 2016 to version 18.104.22.168 where I was unable to select workflows when creating an MPR. The error displayed was The Required Field Cannot Be Empty. The Selected workflow would be cleared when hitting next or submit button.
Further testing identified that you could successfully add workflows from the first page of the paginated list of workflows, but not from subsequent pages of the paginated list of workflows.
The resolution to the issue was to uninstall .Net 4.6 (KB3045563) after applying the MIM 22.214.171.124 patch which allowed workflows to be selected and successfully saved to the MPR from all pages of the paginated workflow list.