2.03k Game freezes when Seleucid takes last Nabatean fortress (Dedan) and latter goes horde.

The Nabatean horde appears to spawn on the Dedan fortress, which I think causes the freeze up.
I think it's a general scripting error but if you can't easily find the cause or reproduce it I can provide the savegame.

To my eyes the game log doesn't provide any clues, but this I can also provide if needed.

Ah, nevermind. I read a few more bug reports and noticed that factions going horde will take some time. So I waited and eventually the game became responsive again.

Yes, to confirm when a faction hordes, it can take a long time (up to 30 minutes or even more) for the game to finish processing the outcome.