Check if it also happens without addons/workshop mounted, it could be a render flag bleed
#Weird Lighting Issue
hollow belfry
sturdy anchor
I give 99.9% that all these bugs are due to the use of the name of the sun and all sorts of mods for editing shadows. The Source Engine is not designed for this.
ornate anchor
Could be an issue with leaks on compile. If you’ve still got the VMF, recompile it and check logs. I’ve also seen env_projectedtexture interact poorly with VRAD’s calculations in addition to cubemaps acting funky with lighting, rebuilding it can resolve the issue sometimes. And as others have stated above, naming your env_sun can also cause unforeseen consequences 🤙🏼
weak pond
If you're especially superstitious like me, you could place water down in a bucket and see if it's wonky. If it is, I assume it's a mapping error.
bright dagger
In my experience, this actually has to do with a poorly coded overlay - disable EVERY overlay (Steam, Discord, Overwolf) and give it another go
The symptoms in the vids match what I dealt with exactly
tall nexus
man thinks this is a gmod update regression 💀