I updated my iPad Pro from recent iOS 11.0.0 to 11.0.2 and found out that the external display is crashing as soon as you connect it. The iPad turns black and you you see the loading symbol until the device restarts.
We thought this issue only occurs on older iPad models like Air 2 and below but with the latest update this issue also affects the latest models.
If you have any serious performance coming up i would recommend to wait till this issue is fixed by Apple with iOS 11.1
I immediately checked the new public beta of iOS 11.1 and the external display works again on all models.
Please have patience until this patch goes live in the end of October.