In some cases Crowd might erroneously detect another instance is accessing the Crowd database and shut down

When running Crowd Server 3.0.0, the functionality to detect if there are multiple Crowd instances connected to the same database might trigger a false positive. This will cause the instance to be blocked with a message like

The Crowd database (database-url) is being updated by another instance. The instance IP is 1.2.3.4. Please make sure all the instances connected to this database are Data Center instances and have clustering enabled.

Workaround:
You can set the system property crowd.check.concurrent.instances.interval to 0 to disable the check.

This can be achieved by changing the CATALINA_OPTS environment variable when running Crowd:

CATALINA_OPTS=-Dcrowd.check.concurrent.instances.interval=0