In situations where with ios9 I could rely that I put my headphone on and push the button on the headphones the correct thing would start playing immediately this got worse with ios10, things started to not work always and with ios11 it's so bad that I can't bring myself to spend money on a new ios device. When my 6s dies I hope there will be something other then the duopoly available.
https://beta.apple.com/sp/betaprogram/redemption (Apple ID login required)
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[1] When I rotate the phone, half the UI elements react to the rotation and update, but the other half of the UI remains at the previous mode. So I have a UI which is half landscape, half portrait. Depending on the mood of the iPhone, the UI will fix itself in either a second, 5 seconds, or not until I restart the app.
Rebooting helps. Feels like trying to use Windows on a cheap desktop to watch an HD movie in 2001.