Here's an issue I was involved in only on the very fringes. ColdFusion restarts of specific instances on a multi-install Linux server were taking forever due to session replication, but we could not see that replication was actually turned "on". There was no cluster and no admin setting indicating replication was on, but the log files definitely indicated sessions were being restored after a restart. The fix actually comes from ColdFusion Guru Brian Ghidinelli.
Brian's post is quite thorough so I won't indulge in my usually wordy explanations. Suffice it to say that when you create a new instance the jrun-web.xml file needs to be copied to your new instance specific /web-inf directory and configured with session replication off. If it's not there, copy it from the /cfusion instance. Apparently on Linux this file is not appropriately copied into individual instances that you create, so CF reverts to the default behavior for all settings in that file (meaning replication is on but you can't see how). See Brian's post for very specific instructions.