With Hotfix #4
When summoning Beastmaster Animal Companion it triggers the start of combat even when no hostiles are around.

Also the Bear Druid is hostile to the party when freed. Cannot progress quest line as desired.

Did you throw rocks at him?

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 ^^'