I've been working on this file for a while with no problems, until now. In Material Preview mode all my objects appear bright white, apart from the trees at the back, which are black. All the other viewports seem to be working as they should and i can still render an image with all materials in place. I just cant see them anymore in Material Preview.
Happens to me too, I usually solve this way:
Select EEVEE as renderer if it's not already, then go to Indirect Lighting and Delete Lighting Cache, then bake it again.
At this point switch between shading view modes, it should get fixed.
We should probably mark this as a bug, not 100% sure about it but looks like it.