Custom Textures and Rendering Resolution bug

[LunaMoo]

Just a guess, but if one of the other settings you changed was forcing "nearest" texture filtering(or if game does that on it's own to affected textures), resolutions with lower pixel density will have such artifacts by design, that's just how this filtering works with stretched textures(commonly fonts) where some "pixels" will be squished, while others stretched out, effectively turning what should be square into rectangles and does that pretty randomly so it usually looks exactly as the problem on your screenshots.