So I've recently been doing veteran HoF 2-3 times a week.
The 1st boss, the hunter killers, I get straight booted to login about every 5 minutes on my healer and every 10 on my tank.
The only other time I've been kicked to login is the Reactor, Reducer and Reclaimer when they all drop below 20% and recover from the stun. Happens almost as often.
While getting booted to login I can tell it happens a few seconds beforehand. My character vanishes from screen and all other characters stay still for 1-2 seconds motionless.
Another bug is that on my healer I can not place Illustrious Healing (Grand Healing morph). A cut animation displays with the staff but the full animation never plays out and the skill is not cast. I can however cast other abilities, but then I get kicked to login about 15 seconds later.
It sometimes happens to others in vHoF, however it really affects me on the 1st and 4th boss.