We have a chat on the disroot server (firstname.lastname@example.org) and some of the members have reported their messages not being sent. I have not had that personally happen but at least two people in our chat have. One of them said to me:
"I find it strange an XMPP server would stop accepting messages ounce it gets overloaded. I'd expect the messages per second to start slowing down, and sending a reply that the 'chat is too busy' to end up taking a similar amount of resources as just delivering the message normally"
Might be something to look into. Thanks in advance!