How to read RGBA from any texture?

Here’s one run where one tile is the proper resolution, but the others are not.

But when I save it, it changes to this:

The exact same code generates all the tiles. The material to render the texture uses LOD0. Oh wait… these can be streamed in, right? That’s likely the problem. Let me force them to load all LODs. Thing is I have like 50 textures. I don’t want to change them one by one.