poezio renders illegal body with mixed content
<message xml:lang="en" type="groupchat" to="email@example.com/poezio-C7iY" from="firstname.lastname@example.org/balu_der_baer" id="b23f6efec2cf4ac2ad23d7da18fb7367"><body>When a message is archived, the server MUST add an <stanza-id /> element as defined in Unique and Stable Stanza IDs (XEP-0359)  to the message, which informs the recipient of where and under what ID the message is stored. When doing this the server MUST follow the business rules defined in XEP-0359.</body><stanza-id xmlns="urn:xmpp:sid:0" by="email@example.com" id="2019-09-11-e360996b290c9aae" /><origin-id xmlns="urn:xmpp:sid:0" id="b23f6efec2cf4ac2ad23d7da18fb7367" /></message>
This stanza was displayed as "When a message is archived, the server MUST add an " in the MUC.
According to https://xmpp.org/rfcs/rfc6121.html#rfc.section.5.2.3
The body element MUST NOT contain mixed content (as defined in Section 3.2.2 of [XML]).
This is probably a slix issue even.