Same thing occured in both my EB campaigns (so far).

I gave up my Epeiros one in 179bc three provinces away from victory, CTD on the Ptolemaic turn. Tried to play again from 182BC, extensively changing my moves, but still... CTD, Ptolemaic turn 179BC.

Took me two months in my Pahlava campaign to dominate the middle-east and eliminate the Saka Rauka, I should soon be able to field Grivpanvar (at last!) and boom, CTD, Ptolemaic turn, 179BC.