It is quite well known that the (android) app(s) are behind on which MathJax version they are currently using (see here for an example). I find this very unfortunate as many of the newer features, especially the unit helper of mhchem are causing errors. As much as I dislike that, I'd argue to not pay attention to that at all, but to focus on the desktop website instead. (I guess the app users are still the minority and most of them also use the main website, and I think this will remain the case for the time being.)
This came to my attention, as there was an approved edit which changed
\to. I think these kind of arrows have distinct different meanings in mathematics and are not interchangeable, just as we do not use mesomeric arrows for an equilibrium.
If we wait until the apps catch up, we might have to wait for a long time and it will block further development of MathJax and mhchem.
Any opinions on the matter?