UDP mode does not listen UDP

[danilasar]

Today I was confused by a strange behaviour. I wrote the config:

{
	"Transport": "udp",
	"ProxyBook": {
		"ss11443": [
			"udp",
			"127.0.0.1:11443"
		],
		"ss12443": [
			"udp",
			"127.0.0.1:12443"
		]
	},
	"BindAddr": [
		":443"
	],
	"BypassUID": [
		"..."
	],
	"RedirAddr": "mail.google.com",
	"PrivateKey": "..."
}

Then

/usr/bin/ck-server -c /etc/cloak/server.json

And ss -lpn | grep 443 outputed me that result:

udp   UNCONN 0      0                                              0.0.0.0:12443            0.0.0.0:*    users:(("ssserver",pid=52523,fd=12))                             
udp   UNCONN 0      0                                              0.0.0.0:11443            0.0.0.0:*    users:(("ssserver",pid=52523,fd=10))                             
tcp   LISTEN 0      1024                                           0.0.0.0:11443            0.0.0.0:*    users:(("ssserver",pid=52523,fd=9))                              
tcp   LISTEN 0      1024                                           0.0.0.0:12443            0.0.0.0:*    users:(("ssserver",pid=52523,fd=11))                             
tcp   LISTEN 0      4096                                                 *:443                    *:*    users:(("ck-server",pid=56385,fd=3))

Is it okay that ck-server doesn't listen UDP and listens TCP instead? I have a suspicion that it is a reason why my UDP packages remain unanswered. The same problem I've got with a quic transport.

P. S. I don't use any firewall, nc -vu at local & tcpdump -n udp port 443 at server works.