I often advise to write code on "obsolete" tech. It makes every bit of cruft obvious.

I test all of my apps on an old Moto G, second generation, on throttled mobile internet (64kbps).

That’s the average worst case user.

This also means I notice massively if an app has hardcoded timeouts, or loads massive amounts of data.

Pretty much, yeah. I never noticed it on campus because I was sitting on a 10 megabit connection.

That added an extra dimension to the confusion because I was sure this never happened when I was on campus, only when I was sitting 300 miles away. It was still happening if I had bothered to look at the network stats, just not enough to entirely saturate the connection.