Currently testing for a 10.3.x -> 11.2 agent deployment

I know you can't modify stages once a deployment has been initiated, so we have made a group a stage member, with a view to being able to add devices to the group...

Tried whilst the stage is still in progeress - no joy, just seems to have settled on an initial static read of the membership
So, cancelled the deployment and re-issued the staged deployment, just cycled through pre-ceding stages with no issues
However, the stage in question doesn't appear to acknowledge the new group members - just shows the original members as successful and no pending.... Now sitting there "Pending Admin Action" to move to next stage

Is there a way to force the deployment to re-evaluate the stage membership?