So upon further investigation, I believe it's an issue with Blubbo's mods. Most trees added from a Blubbo mod seems to be having issues with seasonal LODs. How would I fix this?
But I've also noticed the Whiterun terrain LOD doesn't seem to be changing in winter either, and also as you can see some of the roofs aren't snowed over in the LOD.
Also, I checked Blubbo's files and there's no premade LOD, so there shouldn't be anything getting in the way.
Problematic Tree LOD
Reference of Tree
Whiterun LOD
Whiterun Reference of Tree
Logs
https://ufile.io/f/yqdg1