Why do my answers in the "Math" category only appear on my desktop , and not on other devices? e.g. Notebook, tablet, etc.?

Do they have links? That may cause "ghosting" of an answer. So may excessive symbols, which is obviously a problem if you are answering Math questions by showing your work. Find an answer of yours that has the issue you mention, see if it has a lot of symbols. Temporarily delete the excess symbols, put a simple answer - and see if that fixes the problem. If it does, you will at least know what is causing it. After that, you will have to figure out a solution, sorry.

I doubt anyone has a good answer for this. I doubt very much that switch to desktop as anything to do with you not being able to see the answers. But give it a try. I and others would be interested to see what you find. The desktop mode only gives you more options.