I believe I am having the same issue I find in game that at first it play smooths but then gets a massive dip for a second usually when casting an ability with the AOE on the ground or when it does the shadow radius thing for ranged abilities or when I enter a slightly different zone this seems to be a new issue as when I was playing a few months ago. All was well from what I remember only when I loaded in was it a bit laggy.
Specs
Graphics card: Intel Arc A770 (16GB VRAM)
CPU: 13th Gen Intel i7 - 13700F
Ram: 32GB
Installed on a NVMe SSD