I might be going crazy but...within the past two or three weeks, I have started to notice an abundance of "joining encounter in progress" messages while in dungeons. Like...while running the actual dungeon, not while joining a pug group in the middle of things.
Last night, I was running Frost Vault and someone in the group ran directly to the first boss at the beginning and before I could even get my bearings, I was jumped smack into the middle of the boss fight. Happened twice more in that dungeon...once while I was opening a chest and then again when I got turned around and accidentally went the wrong way. To make it extra special, it seems to drop me right in the middle of the hottest part of the fight--so I'm dead before I can even draw my weapons.
Is this a "feature" that came with a recent patch? Or is there some setting somewhere that I can turn off?