Using Crowd in a Cluster is Not Supported
Atlassian does not support clustering of Crowd, and we have not yet scheduled cluster support into the Crowd roadmap. The reason is that clustering problems are hard to diagnose and we do not have the expertise in-house to support the many possible configurations.
There is a feature request in CWD-1053. You can vote for the feature request, and "watch" it to receive progress reports.