After upgrading Quick Connect Sync Engine, scheduled workflows do not run.
Sometimes there is an issue during the upgrade process where the old Quick Connect service entries are not removed when the information is imported. Since the new Quick Connect service will have a new GUID, there ends up being duplicate service entries in the database with different GUIDs. The scheduled workflows keep their configurations to be run on the old service GUID, causing them to not run, as it doesn't match the new service GUID.
Modify the schedule on each scheduled workflow and select the other service from the drop-down. You will see the service name listed twice.