Had this happen several times now, from Vet Maelstrom (during event), Vet RoM, to Wayrest Sewers II today. Basically, just like that bug from roughly a month ago where normal dungeons (pledge dungeons) were scaling harder than vet.
Today, Wayrest II some mobs were 1-hitting us and acted like they had damage shields up and were 3-5 times harder to kill or impact, then next area mobs were going down in 2 hits. The bosses actually were opposite, and acted more like normal difficulty instead of vet and were burned quickly on HM.
I'm not sure how the difficulty is scaling exactly, but it's clearly bugged in some instances, making it HARDER than intended.