I have had two instances where my game became unplayable. In the first case, I finished the campaign and upon loading End of Time, my character wasnt present and I couldnt take any actions. In the second instance, I was doing an echo and experienced sever rubber banding and odd situations where I would Lunge at an enemy, and I would see their health bar change, but my character would just stay stationary and be nowhere near the target.
In both cases, I re-logged on and both times there was another human person in my end of time instance. They were as confused as I was.