My iphone 6 screen won't rotate

i recently upgraded my iphone 6 to iOS 11.01 and find it nicely working, but after i got used to it, some problems occured:

1. the delay i got when i turn on the screen. When i push the power button, the screen goes black a couple milisecond before it turns on, it actually shows the assistive touch button before fully turned on

2. i can't watch videos in landscape on any apps except youtube eventhough i had the potrait orientation lock off (this is a serious problem for me because it was part of my job to watch videos)

anyone got a solution for this? or am i doing this wrong? or is this some kind of unsolved bugs in iOS 11 for iphone 6? i don't know, you guys tell me.

thanks.