Quartz troubleshooting

Problem:
Quartz in clustered mode, nodes are sync via db.
There are many lines like these in logs:
[2015-07-04 00:00:01,620]  WARN [QuartzScheduler_scheduler-prov011435933239135_ClusterManager] (JobStoreSupport.java:3298) - This scheduler instance (prov011435933239135) is still active but was recovered by another instance in the cluster.  This may cause inconsistent behavior.

"The most probable cause of such a cluster-related error is having cluster nodes with system clock not synchronized."

Ref:
http://quartz-scheduler.org/documentation/faq

https://confluence.atlassian.com/display/JIRAKB/This+scheduler+instance+(%3Cnodename%3E)+is+still+active+but+was+recovered+by+another+instance+in+the+cluster

https://stackoverflow.com/questions/15701417/strange-behavior-of-quartz-in-cluster-configuration