Comment 24 for bug 1874831

That simple post+sub also works fine unfortunately:

root@f:~# curl --request POST --data "test message" http://127.0.0.1:80/pub
queued messages: 2
last requested: 6 sec. ago
active subscribers: 0
last message id: 16367017

root@f:~# curl --request GET http://127.0.0.1:80/sub
test message

Using your linked examples (thanks) I got

curl -i --header "Content-Type: application/json" --data '{"message":"test 1"}' http://localhost:80/pub?topic=one
HTTP/1.1 202 Accepted
Server: nginx/1.18.0 (Ubuntu)
Date: Fri, 12 Nov 2021 07:25:06 GMT
Content-Type: text/plain
Content-Length: 101
Connection: keep-alive

queued messages: 3
last requested: 97 sec. ago
active subscribers: 0
last message id: 1636701906:0

root@f:~# curl -i --header 'Accept: text/event-stream' --header "Content-Type: application/json" --get --data-urlencode 'payload={"topics":["one","two"]}' http://localhost:80/sub
HTTP/1.1 200 OK
Server: nginx/1.18.0 (Ubuntu)
Date: Fri, 12 Nov 2021 07:26:09 GMT
Content-Type: text/event-stream; charset=utf-8
Connection: keep-alive

: hi

id: 1636701724:0
data: test message

id: 1636701787:0
data: test message2

id: 1636701906:0
data: {"message":"test 1"}

id: 1636701939:0
data: {"message":"test 2"}

This latter one even works to stay active and further messages posted later arrive here.

Still no sign of the reported breakage.
So it must be part of the setup/config that is done I guess ...