On Server 2003 32bit, using LDAP for users and groups.
I cleared all caches for Openfire 3.7.1 (really I only wanted to clear group cache, but I was lazy).
After that, it would not show anyone in the contact list of a newly logged in user, unless their presence had just been updated. Sometimes, even after a user showed up, they would later disappear until their presence updated again. Of a list of about 30, I was only seeing 4-5 users at a time. I waited about 30 minutes but nothing improved.
Restarting the Openfire service fixed the issue.