When gliders take a sudden turn in behavior like this, it can sometimes be a health issue. I'd take em to the vet and have them both checked out including fecals.
If health is ruled out from the vet and fecals are clear...... it could be they are having a shift in dynamics, one trying to become the dominant glider.
Sometimes gliders that have always gotten a long, just don't get a long anymore. It happens, and when it happens the owner needs to intervene because the gliders are trapped together. In the wild when this happens one of them simply leave the colony and find another one. They can't do that in captivity.
They may just be having an argument...
There are a few things it could be, but ruling out health issues is the first thing to do in most of these cases.