Based on debugger info, it turns out the image request is missing a token parameter which is why images are not being shown. I'm not sure why the token is not being generated
This is a big issue with moodle for Android and a lot more issues keep showing face, I have not been able to get this to work at my end too, I will probably make a post and highlight all the issues I have noticed so far with he custom or branded moodle app.