The good news is that your problem reproduces.
You have 2 support ships attacking a starbase. Hivebase One (a carrier) and a Probe (which has no attack).
Both ships are set to hang back, Hivebase One because it's a carrier and the Probe, because it can't attack anything.
Each round both ships look at each other and effectively say, "you go ahead" and neither does so they are both sitting stationary.
On the other side is a starbase, it cant move.
So they are sitting out of range of each other and the battle never ends.
If you just pull the probe out of the fleet it will work. But the code is supposed to check for this (so its a bug). We are looking into it.