retrieving a group that does not show up as being deleted, either as an owner or admin

I created a plan in Planner and assigned members to the plan.  Created tasks, buckets, etc. Confirmed a member was able to see the plan.  When I logged into planner again the group is not there and a message saying it had been deleted came up.  Neither I or any other member deleted it.  I cannot find it anywhere in deleted groups.  Is it just gone?   Thanks. 

Daniel