Could not get notification state - driver: bad connection

Hi,

Since upgrading grafana to 6.2.3 I’m getting many errors such as:
t=2019-06-26T05:05:18+0000 lvl=eror msg=“Could not get notification state.” logger=alerting.notifier notifier=11192 error=“driver: bad connection”
t=2019-06-26T05:05:18+0000 lvl=eror msg=“Could not get notification state.” logger=alerting.notifier notifier=11192 error=“driver: bad connection”
t=2019-06-26T05:05:18+0000 lvl=eror msg=“Could not get notification state.” logger=alerting.notifier notifier=11192 error=“driver: bad connection”

Any one else encountered such issue?