No, i do not use that items ofcourse =) Beserk is a masterwork material, no MM stands any chance vs 5xHidden Blades on hit. Nor that im using any similiar items like that funny healing amulet. But that was some offtopic, sorry.
Yes, i tried to reload, tried to do to other locations and enter FB again, tried many things. Thus i'd already finished this location, i now think that that was just a bug of damage amplification of one enemy type. Sort of. Maybe that was infinite buff from Walk Softly trial that stayed even with it turned off, maybe some other stuff. Archers in vanilla game are managable.
So, shall i manage it in bug forums? And are there any? :D