I have recently experienced this same issue.
It started when I was running the Market Crash TF in Kallisti Warf. After completing the first mission and exiting, I was kicked out to the login screen. It took me three attempts to log back in before it let me with the character I was on the TF with. I didn't think too much about it until I tried to run a BAF and as soon as everyone accepted and it started to load, I was kicked off the league with an odd mapserve error and then loaded to Oro.
I researched the forums and found this post so I tested this Night Ward with the same affect. I get about 3/4 loaded and then it freezes for a long time and then kicks me to the login screen. No other errors or notifications are given. It takes three attempts to log back in with the same character before I am able to return to the game. After I leave Night Ward, I no longer have issues.
I have tried going full hero and turning off Ultra Mode with no change.
I was able to run Night Ward, Kallisti Warf, and BAF as recently as last week without issue, but as it stands now, any incarnate Praetorian level content is no longer playable.