I had this same bug in the boss fight against Thaos. I have the most recent version, 1.0.3.0524. No mods.
I had this happen twice. The first time, Pallegina becomes totally unresponsive. She won't attack, won't drink potions, nothing. That time, I wasn't paying attention to her - I just left her to engage one of the headsmen. I take out the headsmen with my four remaining characters. Then, my main wizard guy suddenly becomes stuck also. I order him to launch a necrotic lance on Thaos. The next time I check up on him, he is stuck. At this point I reloaded to try the battle again.
On the second attempt, Pallegina becomes stuck after killing one of the headsmen. Afterwards, when only Thaos is left, my main wizard guy again gets stuck. This time I moved him closer to Thaos so he could cast Minoletta's Precisely Piercing Burst. Before my char had reached the intended waypoint, I decided I was close enough and I activated the sixth-level Minoletta spell. My char started twitching and flickering, as if he was still trying to reach the waypoint. Then he became totally inert. No problem - I was able to slay Thaos with Kana, Sagani and Durance. I'm glad this bug didn't manifest any more during the game, just at the end.
I'm quite sure you can replicate this bug during the final fight. So far the characters to become stuck were Pallegina and my main guy on both times.
Here's the link to the Save Game.