systemd-timesyncd无法接收NTP服务器回复（超时）的原因排查求助

大家好，我在Lubuntu 22.04上启用了systemd-timesyncd.service服务，用来运行systemd-timesyncd守护进程。现在遇到个问题想请教各位：

我先查看了这个服务的状态，执行的命令是：

systemctl status systemd-timesyncd

得到的输出如下：

● systemd-timesyncd.service - Network Time Synchronization
Loaded: loaded (/lib/systemd/system/systemd-timesyncd.service; enabled; vendor preset: enabled)
Active: active (running) since Thu 2023-07-06 12:21:43 CEST; 2min 54s ago
Docs: man:systemd-timesyncd.service(8)
Main PID: 1917 (systemd-timesyn)
Status: "Idle."
Tasks: 2 (limit: 2030)
Memory: 1.3M
CPU: 201ms
CGroup: /system.slice/systemd-timesyncd.service
└─1917 /lib/systemd/systemd-timesyncd

lug 06 12:21:55 ceia-te systemd-timesyncd[1917]: Timed out waiting for reply from 185.125.190.57:123 (ntp.ubuntu.com).
lug 06 12:22:05 ceia-te systemd-timesyncd[1917]: Timed out waiting for reply from 185.125.190.58:123 (ntp.ubuntu.com).
lug 06 12:22:15 ceia-te systemd-timesyncd[1917]: Timed out waiting for reply from 185.125.190.56:123 (ntp.ubuntu.com).
lug 06 12:22:25 ceia-te systemd-timesyncd[1917]: Timed out waiting for reply from 91.189.94.4:123 (ntp.ubuntu.com).

从输出能看到服务是正常运行的，但尝试连接NTP服务器ntp.ubuntu.com时一直收不到回复，反复出现超时提示。不过我用ping测试这个服务器是能通的，执行的命令是：

ping ntp.ubuntu.com

输出如下：

PING ntp.ubuntu.com (91.189.94.4) 56(84) bytes of data.
64 bytes from pugot.canonical.com (91.189.94.4): icmp_seq=1 ttl=53 time=30.0 ms
64 bytes from pugot.canonical.com (91.189.94.4): icmp_seq=2 ttl=53 time=29.8 ms
64 bytes from pugot.canonical.com (91.189.94.4): icmp_seq=3 ttl=53 time=29.8 ms

另外，我检查了iptables防火墙，它处于未激活状态，执行命令：

sudo iptables --list

输出显示所有链的策略都是ACCEPT：

Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

现在我实在搞不懂，为什么timesyncd客户端就是收不到ntp.ubuntu.com的回复呢？有没有大佬能帮忙分析下原因？谢谢！

备注：内容来源于stack exchange，提问作者User051209