Docker not extending thin-pool based on /etc/sysconfig/docker-storage-setup

Issue

The docker was configured to use device-mapper and use auto-extend as following

STORAGE_DRIVER="devicemapper"
DEVS=/dev/sdc
WIPE_SIGNATURES=true
VG=dockervg
AUTO_EXTEND_POOL=true
POOL_AUTOEXTEND_THRESHOLD=50
POOL_AUTOEXTEND_PERCENT=20

But the VG dockervg is not extended in case that it reach the threshold.

The output of dm-event during the tests

[root@unused ~]# journalctl -fu dm-event.service
-- Logs begin at Mon 2018-03-12 08:38:37 GMT. --
Mar 12 11:02:24 unused systemd[1]: Started Device-mapper event daemon.
Mar 12 11:02:24 unused systemd[1]: Starting Device-mapper event daemon...
Mar 12 11:02:24 unused dmeventd[10316]: dmeventd ready for processing.
Mar 12 11:02:24 unused lvm[10316]: Monitoring thin pool dockervg-docker--pool.
Mar 12 11:02:24 localhost.localdomain lvm[18416]: WARNING: Thin pool dockervg-docker--pool data is now 81.40% full.
Mar 12 11:03:24 localhost.localdomain lvm[18416]: WARNING: Thin pool dockervg-docker--pool data is now 87.50% full.
Mar 12 11:04:24 localhost.localdomain lvm[18416]: WARNING: Thin pool dockervg-docker--pool data is now 92.42% full.