Legitimate bug report: "this bug is only reproducible when tethered to a phone".

I've had this before. Many cellular providers in the UK proxy all mobile traffic. This proxy performs several "optimisations" to the requested page including sometimes inlining or compressing Javascript. I've had these "optimisations" break a page on more than one occasion.

@aaron that would be the case except it was an restful API request. Or best guess is it's a latency issue with the tethering