You probably used Openfire, known to be a memory hog and a bit unstable.
Simply go for prosody and you should be fine (ejabberd should also be OK). Some newer XEPs which you may want to have with Conversations are not supported OOTB in prosody (yet) but there are plugins distributed separately [1][2].
Yes that was the culprit! OpenFire sounds like it... I wanted something simple to setup, without too many terminal incantations. Thanks for the information, it's invaluable.
[1] https://modules.prosody.im/ [2] https://prosody.im/doc/installing_modules