The has now been fixed in Mosaic version 22.2
A bug has been introduced in Mosaic 22.1 and persists to 22.2 which means that worksteps which have a future scheduled date (workstep status is future) are not returning to Mosaic successfully from the Mobilise app or the Mosaic portal. This applies to worksteps where the scheduled date is set either when adding a next action with a future date or when reassigning a workstep and adding a future date for completion.
Workaround
Worksteps with a future scheduled date can be reassigned with a start date of today prior to being sent to Mobilise/Portal
Or
Worksteps can be started and saved in Mosaic and then sent to Mobilise/Portal in incomplete status, which will allow them to be returned.