This is the same on my iPhone 5s, the volume bars totally gone and I never updated anything either. I have an iPad mini and nothing changed there so I don't know why this has happened. Let me know if you find out what happened
@user-removed thank you, yes the volume button is no longer a part of the Now Playing screen. To change the volume, you can use the hardware volume buttons on your device. That should work including when AirPlaying as well.
If you use Connect, then the volume bar is available to change the volume on the device that you are controlling.
I know have the some problem since a recent update. Volume control on iPad is just a line. Is in lock screen put not app / now playing screen. This is stupid. This needs sorting. Dont fix what isn't broken etc. Apple Music and Amazon music both have this so why have you taken it out!