Please, read this description [1] and follow https://issues.jboss.org/browse/MODCLUSTER-430 for details. This bug is deeply tricky and it has been around for quite some time. It's actually linked to Apache HTTP Server mod_proxy code integration. We may even speculate whether it might be the root cause of some other mod_proxy integration issues, such as MODCLUSTER-391. [1] https://github.com/modcluster/mod_cluster/pull/119#issue-45463288