This is because there are rows being delete from the rows list while looping over them

https://github.com/aerogear/aerogear-simplepush-server/blob/c8dde71a5eb94ae53c3ab1057ba90ecbe8991745/datastores/couchdb/src/main/java/org/jboss/aerogear/simplepush/server/datastore/CouchDBDataStore.java#L228

replace this loop with a while iterator and the call rows.remove(row) with iterator.remove()

This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira