I don't know why they are doing this but I would start by adding a second sleeping pouch.
Our 2 colonies both have 2 sleeping pouches. this way one or more can have another sleeping area. I would say 90% of time they are all together, but from time to time some will chose to sleep separate.
We had even 2 pouches with our lone glider but one is in the wash for now.
Another thing to think about is a vet visit, I have read sometimes a sick glider can get chased away.