This has happened before, it was ruled out by my guild to be lag for the server.

We had an issue with Turn 2 where things hadn't changed in patch notes or anything but it felt as if the boss was buffed. Another raid team we are friends with said they also had the issue, but their friends didn't.
Apparently it was as simple as re-entering the instance to fix it, but after that night we never had an issue again.

Just a bad night for the servers really, or that individual instance coughing up a bit of bugs.