Version: Chrome 51.0.2693.2
OS: Android 6.0.99; Build/NPC91K
Devices: Nexus 5X, Nexus 6P, Nexus 9

What steps will reproduce the problem?
(1) Go to https://webbluetoothcg.github.io/demos/playbulb-candle/
(2) Click "Connect" button, pick nearby Candle
(3) Pick a color

What is the expected output?
Candle should change color.

What do you see instead?
It's not. writeValue doesn't resolve the first time.
Next time, it fails with JS error "Uncaught (in promise) DOMException: GATT operation already in progress."

Here's the adb log:

05-17 19:57:48.177  3170  3821 E bt_att  : GATT_Write Illegal param: conn_id 5, type 00,
05-17 19:57:48.177  3170  3821 E bt_btif : No pending command