As a web developer iOS is the most infuriating platform at the moment for me. There are some random nonstandard features. Just this last month I had an issue with ios "low power mode" causing webkit to throttle all browser animation frame requests by half, with no way to override or even check if it is on. There are open complaints and issues about this going back years but nobody can change it without Apple's blessing, which they don't give, so it affects every browser on iOS with no recourse.
I have had tons of iphone browser specific issues and I am pretty sure their platform monopoly is a big part of why they go ages without being addressed. If there was real competition on the ios browser market they might push each other to do better by comparison.