On my laptop (macOS), $$\mathbin{\rlap{\,\,\bullet}\triangle}$$
renders as
On my phone (Android), however, the same code (i.e. $$\mathbin{\rlap{\,\,\bullet}\triangle}$$
) renders as
(Note that the size difference is because of the difference in image size, not because of MathJax.)
Why does MathJax render differently on different devices? Is this a MathJax bug, an SE bug or a local bug, and is there a way to fix it?
You can check what it looks like here in this post for you: $$\mathbin{\rlap{\,\,\bullet}\triangle}$$
Edit: It seems that the rendering is different on my laptop and phone only when using the HTML-CSS renderer.