I’ve some difficulties connecting to open_chat@. I first thought that the new Openfire version does not longer process stanzas in-order. But I also see things like this in Poezio’s XML console:
12:02:33 IN <message to="flo@geekplace.eu/bbcd6928-5a72-4eee-b00d-006b4c2e5ae5" id="d560afbe-d4e0-4415-81df-f192cae7cfa9-3316" xml:lang="en" from="open_chat@conference.igniterealtime.org/Flow" type="groupchat"><composing xmlns="http://jabber.org/protocol/chatstates" /></message>12:02:35 OUT <message to="open_chat@conference.igniterealtime.org" id="d560afbe-d4e0-4415-81df-f192cae7cfa9-3317" xml:lang="en" type="groupchat"><body>Guus, ^</body><inactive xmlns="http://jabber.org/protocol/chatstates" /></message>
12:02:35 IN <message to="flo@geekplace.eu/bbcd6928-5a72-4eee-b00d-006b4c2e5ae5" id="d560afbe-d4e0-4415-81df-f192cae7cfa9-3317" xml:lang="en" from="open_chat@conference.igniterealtime.org/Flow" type="groupchat"><body>Guus, ^</body><inactive xmlns="http://jabber.org/protocol/chatstates" /></message>
12:03:12 OUT <iq to="open_chat@conference.igniterealtime.org" id="d560afbe-d4e0-4415-81df-f192cae7cfa9-3318" type="get"><query xmlns="http://jabber.org/protocol/disco#items" /></iq>
12:03:12 IN <iq to="flo@geekplace.eu/bbcd6928-5a72-4eee-b00d-006b4c2e5ae5" id="d560afbe-d4e0-4415-81df-f192cae7cfa9-3318" from="open_chat@conference.igniterealtime.org" type="result"><query xmlns="http://jabber.org/protocol/disco#items"><item jid="open_chat@conference.igniterealtime.org/alameyo" /><item jid="open_chat@conference.igniterealtime.org/gakwaya" /><item jid="open_chat@conference.igniterealtime.org/vanitasvitae" /><item jid="open_chat@conference.igniterealtime.org/Guus" /><item jid="open_chat@conference.igniterealtime.org/Flow" /></query></iq>
12:10:15 IN <presence to="flo@geekplace.eu/bbcd6928-5a72-4eee-b00d-006b4c2e5ae5" from="open_chat@conference.igniterealtime.org/dwd"><c xmlns="http://jabber.org/protocol/caps" ver="RWqhJlsL3GMRIM4xuyp3v5x6PoY=" hash="sha-1" node="http://conversations.im" /><x xmlns="http://jabber.org/protocol/muc#user"><item jid="dwd@dave.cridland.net/tablet" role="moderator" affiliation="owner" /></x><nick xmlns="http://jabber.org/protocol/nick" /></presence>
12:16:32 IN <presence to="flo@geekplace.eu/bbcd6928-5a72-4eee-b00d-006b4c2e5ae5" xml:lang="en" from="open_chat@conference.igniterealtime.org/Flow" type="unavailable"><c xmlns="http://jabber.org/protocol/caps" ver="FgVu3eKRNU9FLxn8d8nq1KogkmY=" hash="sha-1" node="http://slixmpp.com/ver/1.2.4" /><x xmlns="vcard-temp:x:update" /><idle xmlns="urn:xmpp:idle:1" since="2017-
10-29T11:59:44.883384" /><x xmlns="http://jabber.org/protocol/muc#user"><item jid="flo@geekplace.eu/bbcd6928-5a72-4eee-b00d-006b4c2e5ae5" role="none" affiliation="owner" /></x><nick xmlns="http://jabber.org/protocol/nick" /></presence>
i.e. a unavailable presence out of nowhere.