It’s not that the textures are disappearing, it’s that the mesh isn’t being rendered when offscreen. It’s kind of a weird bug and it’s due to the Animator. On the Animator component you can set it render at all times or only render when it’s visible on screen. This doesn’t always work though so usually I would recommend changing it to always update.

I’m not sure where you updated the “Update when Offscreen” settings, but this probably does the same thing.