Bluetooth does not work

Tags: #<Tag:0x00007f617135d200> #<Tag:0x00007f617135d138> #<Tag:0x00007f617135d048>

Hi guys. I am using openHAB2.4 on my Ubuntu 16.04, trying to search for Bluetooth device using the bluetooth binding. My Bluez is 5.45. When I seach for devices and look at the log, it outputs:

[ERROR] [ernal.discovery.BlueZDiscoveryService] - Cannot access BlueZ stack due to permission problems. Make sure that your OS user is part of the ‘bluetooth’ group of BlueZ.

However I checked my current user by openhab-cli info, it shows

Version: 2.4.0 (Build)
User: openhab (Active Process 2150)
User Groups: openhab bluetooth

Directories: Folder Name | Path | User:Group
----------- | ---- | ----------
OPENHAB_HOME | /usr/share/openhab2 | openhab:openhab
OPENHAB_RUNTIME | /usr/share/openhab2/runtime | openhab:openhab
OPENHAB_USERDATA | /var/lib/openhab2 | openhab:openhab
OPENHAB_CONF | /etc/openhab2 | openhab:openhab
OPENHAB_LOGDIR | /var/log/openhab2 | openhab:openhab
(Here I hide the ip and port)

And I also checked the user group information, which shows that:
openhab : openhab bluetooth
So I successfully add it into the bluetooth group. But I don’t know why it can not work. Can anyone help me figure it out?