Did the guards get a buff in U50? I used to be able to melt them solo but now they're hitting harder and tanking more damage. In blackreach on adventurer veterancy.
One thing you might want to do is check your Death Recap. If it says "Improved Fire Torrent" on it, then you've been going up against guards who have been buffed due to the resource getting upgraded to Level 1:
Maybe you already knew that (since it's been part of the game for a long time) and you're talking about something else, but the first time I encountered buffed guards while soloing a resource I was taken completely by surprise at how easily they were able to kill me when I was used to just running up to the flag and killing them without much difficulty.
It's also possible that something about your class passives or various active skills (class, weapon, etc.) got nerfed a bit.
upgraded guards can be tough if there is a lot of them
i think the guards also have some kind of hidden -healing debuff on most of their dots cause i notice that heals seem less effective after getting hit by them
been that way forever though
dealing with guards is actually a moderate challenge in vengeance when your not crazy OP lol
i have my main house (grand topal hideaway) listed in the housing tours, it has multiple target dummies, scribing altar, and grandmaster stations (fully filled out with current game), as well as almost every antiquity furnishing on display to preview them
in progress: acquiring mundus stones (currently only have the thief)