I get slightly different results:
root@oguard:~# mtr -bw -c2 -r ntp.bollar.com
Start: 2020-07-29T14:34:05+1000
HOST: oguard Loss% Snt Last Avg Best Wrst StDev
1.|-- ??? 100.0 2 0.0 0.0 0.0 0.0 0.0
2.|-- bri-pow-que-crt3-be-100.tpg.com.au (60.240.241.1) 0.0% 2 5.9 6.4 5.9 6.9 0.8
3.|-- syd-apt-ros-crt1-be-50.tpg.com.au (203.219.107.74) 0.0% 2 26.0 24.0 22.1 26.0 2.8
4.|-- syd-apt-ros-int1-eth8-3.tpgi.com.au (203.29.134.67) 0.0% 2 24.4 23.2 21.9 24.4 1.8
5.|-- 100ge13-1.core1.sjc1.he.net (216.218.139.233) 0.0% 2 174.1 172.9 171.6 174.1 1.8
6.|-- 10ge7-2.core1.sjc2.he.net (72.52.92.118) 0.0% 2 172.3 171.9 171.5 172.3 0.5
7.|-- e0-36.core2.sjc2.he.net (184.104.192.214) 0.0% 2 174.5 173.7 172.8 174.5 1.2
8.|-- charter-20115-as20115.port-channel2.core2.sjc2.he.net (64.62.153.206) 0.0% 2 173.2 172.9 172.5 173.2 0.5
9.|-- bbr02snjsca-bue-1.snjs.ca.charter.com (96.34.3.108) 0.0% 2 178.7 175.7 172.7 178.7 4.3
10.|-- bbr01rvsdca-bue-8.rvsd.ca.charter.com (96.34.0.177) 0.0% 2 186.5 187.6 186.5 188.6 1.5
11.|-- bbr01dllstx-bue-6.dlls.tx.charter.com (96.34.0.20) 0.0% 2 219.5 217.4 215.3 219.5 3.0
12.|-- crr01ftwotx-bue-2.ftwo.tx.charter.com (96.34.2.33) 0.0% 2 221.1 219.7 218.2 221.1 2.1
13.|-- dtr01kllrtx-bue-3.kllr.tx.charter.com (96.34.112.181) 0.0% 2 216.8 218.4 216.8 219.9 2.2
14.|-- ??? 100.0 2 0.0 0.0 0.0 0.0 0.0
15.|-- 047-051-249-154.biz.spectrum.com (47.51.249.154) 50.0% 2 233.5 233.5 233.5 233.5 0.0
root@oguard:~# mtr -bw -c2 -r --port 123 --udp ntp.bollar.com
Start: 2020-07-29T14:48:51+1000
HOST: oguard Loss% Snt Last Avg Best Wrst StDev
1.|-- ??? 100.0 2 0.0 0.0 0.0 0.0 0.0
2.|-- bri-pow-que-crt3-be-100.tpg.com.au (60.240.241.1) 0.0% 2 6.4 6.1 5.8 6.4 0.4
3.|-- syd-apt-ros-crt1-be-50.tpg.com.au (203.219.107.74) 0.0% 2 22.0 22.1 22.0 22.2 0.1
4.|-- syd-apt-ros-int1-eth8-3.tpgi.com.au (203.29.134.67) 0.0% 2 23.3 23.1 23.0 23.3 0.2
5.|-- 100ge13-1.core1.sjc1.he.net (216.218.139.233) 0.0% 2 172.5 176.4 172.5 180.2 5.5
6.|-- 100ge1-1.core1.sjc2.he.net (184.105.65.114) 0.0% 2 172.0 172.3 172.0 172.6 0.4
7.|-- e0-36.core2.sjc2.he.net (184.104.192.214) 0.0% 2 173.2 172.5 171.7 173.2 1.1
8.|-- charter-20115-as20115.port-channel2.core2.sjc2.he.net (64.62.153.206) 0.0% 2 188.7 180.9 173.1 188.7 11.1
9.|-- bbr02snjsca-bue-1.snjs.ca.charter.com (96.34.3.108) 0.0% 2 175.1 176.8 175.1 178.5 2.5
10.|-- bbr01rvsdca-bue-8.rvsd.ca.charter.com (96.34.0.177) 0.0% 2 186.7 187.3 186.7 187.9 0.8
11.|-- bbr01dllstx-bue-6.dlls.tx.charter.com (96.34.0.20) 0.0% 2 218.4 219.4 218.4 220.3 1.4
12.|-- crr01ftwotx-bue-2.ftwo.tx.charter.com (96.34.2.33) 0.0% 2 223.8 219.5 215.2 223.8 6.1
13.|-- dtr01kllrtx-bue-3.kllr.tx.charter.com (96.34.112.181) 0.0% 2 220.0 219.7 219.3 220.0 0.5
14.|-- ??? 100.0 2 0.0 0.0 0.0 0.0 0.0
I’m not particularly surprised that the last mtr hop doesn’t work when using UDP, because the last hop will be the host itself, and mtr will not be composing a correct NTP packet, so the NTP server should not reply.
I ran up this server as a source on my machine (with burst iburst noselect enabled), and at one point I got enough responses that it could calculate jitter:
47.51.249.154 .PPS. 1 u 34 64 7 230.999 1.714 0.618
But now it has gone back to being unresponsive.
My guess would be that rather than this being a routing problem on the ISP side, the volume of requests going to this server is high enough that it filled connection tracking tables in the host or an upstream firewall.