Import Settings not respected on build (sometimes)

I'm seeing a strange (seemingly random) issue where I've manually compressed a texture via Import Settings to say Max Size: 1024 which gives me a smaller texture at 4.0mb.

However, when I build I see that sometimes the editor log shows the same file is back up to 16.0MB. Maybe 1 out of 4 builds it's 4.0mb. With no changes to the game at all, just executing a new build.