Help needed: UE4’s lighting is completely broken (new and existing projects)

I’m pretty new to UE, but immediately after I upgraded from 4.25 to 4.26, all of the lighting in my projects went totally out of wack (solid red or blue lighting and blown out skies).

This is an example of what that looks like for a totally new project: UE4 4.26.1 bug - Album on Imgur

I completely reinstalled UE4 and restarted my computer, but nothing has worked. Any tips or suggestions as to what might be up?

Thanks for any help you can provide!