Http3 example not working

Bootstrap server works but not the H3App server - tested on Firefox, code version 20.36.0
Not sure what is causing this issue, firefox doesn't have any output.
Server output after uncommented some logging:

yuu@ubuntu-server:~/quic-test$ ./Http3Server
Bootstrapping server Listening on port 9004
Creating socket context with ssl: misc/key.pem
Engine: 0x55973f746ab0
Client Engine: 0x55973f77d090
The port of UDP is: 9004
HTTP/3 server Listening on port 9004
We got no ECN!
Reading UDP of size 1357
We received packet on port: 9004
getting ssl ctx now, peer_ctx: 0x55973f77d010
Key: misc/key.pem
Cert: misc/cert.pem
loaded cert and key? 1, 1
yolo SNI server_name_cb
existing name is: (null)
set name is: YOLO NAME!
simply returning old ctx in sni
select_alpn
OPENSSL_NPN_NEGOTIATED
Engine returned: 0
We got no ECN!
Reading UDP of size 1357
We received packet on port: 9004
Engine returned: 0
send_packets_out: returning 3 of 3
We got no ECN!
Reading UDP of size 42
We received packet on port: 9004
Engine returned: 0
send_packets_out: returning 1 of 1
We got no ECN!
Reading UDP of size 111
We received packet on port: 9004
Engine returned: 0
Context is: 0x55973f745cc0
QUIC socket connected!
send_packets_out: returning 2 of 2
We got no ECN!
Reading UDP of size 317
We received packet on port: 9004
Stream open!
Engine returned: 0
wrote until end, shutting down now!
send_packets_out: returning 1 of 1
We got no ECN!
Reading UDP of size 31
We received packet on port: 9004
Engine returned: 0
send_packets_out: returning 1 of 1
We got no ECN!
Reading UDP of size 32
We received packet on port: 9004
Engine returned: 0
send_packets_out: returning 1 of 1
send_packets_out: returning 1 of 1
We got no ECN!
Reading UDP of size 32
We received packet on port: 9004
Engine returned: 0
We got no ECN!
Reading UDP of size 32
We received packet on port: 9004
Engine returned: 0
send_packets_out: returning 1 of 1
We got no ECN!
Reading UDP of size 32
We received packet on port: 9004
Engine returned: 0
send_packets_out: returning 1 of 1
We got no ECN!
Reading UDP of size 32
We received packet on port: 9004
Engine returned: 0
send_packets_out: returning 1 of 1
We got no ECN!
Reading UDP of size 32
We received packet on port: 9004
Engine returned: 0
send_packets_out: returning 1 of 1
We got no ECN!
Reading UDP of size 32
We received packet on port: 9004
Engine returned: 0
send_packets_out: returning 1 of 1
send_packets_out: returning 1 of 1
We got no ECN!
Reading UDP of size 32
We received packet on port: 9004
Engine returned: 0
We got no ECN!
Reading UDP of size 32
We received packet on port: 9004
Engine returned: 0
send_packets_out: returning 1 of 1
We got no ECN!
Reading UDP of size 32
We received packet on port: 9004
Engine returned: 0
on_conn_closed!
QUIC socket disconnected!
Http3Server: uWebSockets/uSockets/lsquic/src/liblsquic/lsquic_full_conn_ietf.c:3133: ietf_full_conn_ci_destroy: Assertion `conn->ifc_conn.cn_conn_ctx == NULL' failed.
Aborted (core dumped)

Reproduce the failure with Http3Server and Firefox using code version 20.36.0, starting from the server output and the assertion in lsquic/src/liblsquic/lsquic_full_conn_ietf.c:3133. Trace the connection-close path around that assertion and compare it with the successful Bootstrap server; done means Firefox receives output and Http3Server exits without aborting.