I get the occasional stutter now, it's from me running vulkan shaders on linux, which is really the only way I can get valheim to run (recent patch made vulkan shaders stuttery--I might see if I can force it to run compatibility mode for Glorious Eggroll 7.43), so it might be from world saves, might be something cutting in and out like audio but you don't notice it, update drivers, check integrity of files, etc.

Could really be anything. Just because I am also experiencing it, means that my problem could be different from yours

But since we are both suddenly encountering this same problem, I would imagine it's a driver issue or the recent update messed with some graphics performance.