Pixel C Android 7.0 Nougat Bluetooth issue

I have a BLE device with service 128-bit UUID, the UUID is 0000fffd-0000-1000-8000-00805f9b34fb. I can discover the service by app, but can't access any characteristics under it. No any command sent from Pixel C when pressed read/write operation on characteristics. Please investigate and fix it, thanks.

James