Since the U39, and for whatever reason, especially today, lots of people (based on guild and zone chats), myself including, have been experiencing extreme lag events. E.g., several seconds freezes during a boss fight (most noticeable was the High Isle Ascendant Harrower and Executioner bosses in my case).

I was thinking it /might/ be a client-side issue, but then I have encountered one that definitely is server-side.

We've been doing the Unmaker WB daily, so teleported to the Blood Pit wayshrine, I mounted on the 2-rider, another player hopped on as a passenger, and I went north. Shortly after the second road branching off east (a bit over halfway to the boss), I got a loading screen, then I reappeared back near the wayshrine on feet. ... The thing is, my passenger got dismounted and stranded at the point over halfway to the boss, so it could not have been just my client.