Got the same bug. Turns out, it was because one of my companions has killed my pet using the environment.
Steps:
1. Go to the temple ruins, where other adventurers are arguing
2. Start the fight
3. Drive the beastmaster's pet to the shattered floor below the stone block
4. Hit the stone block to drop it on the floor and kill the pet
5. Summon the pet again after the fight
6. Observe that the fight has begun
Only loading the save before this fight fixed the issue.
P.S. Sorry for my English ^^'
