I use a Bose Soundlink II mini bluetooth speaker, AirvideoHD. Up to iOS10 I could press the Play/Pause button on the speaker to play and pause when watching.
Right after updating to iOS11 though, the same button does not pause anymore. If I pause using the AirvideoHD interface on the iPad, I can then press the Play/Pause button on the speaker to play, it's just the pause function that stopped working.
I have an other app with similar issues, like is something changed in iOS11 play/pause code. TuneIn radio for example. The Play/Pause button on the speaker does not pause or play at all after iOS11. I contacted them as well.
The speaker button Play/Pause does work with the iPhone/iPad Music app, and Apple's own Video app. It seems it is an issue with 3rd party apps.