Perhaps some firewall on the way is blocking it, because udp packets from btest are not seen by stateful firewall as established or related, they look like random unsolicited packets. At least that’s the problem I have with udp btest all the time.
I have backed up the config and reset to default, then restore the previous config.
Finally the probelm has gone.
no any firewall rules changed.
Dunno What happened.