Do you still have this issue or not? The "unknown error" was usually caused by intermittent network connection to Apple. If this situation continues to exist please send us your device's information
I dont things here, my connection its stable in the LTE network.
The advice comes from the using environment as below:
1.System device: 11.0.3
2.System version: iPhone
3.APP version：1.4.1 (1204)