Odd - I'm getting the same! (RB493G v5.5) Except mine is trying to talk to another MT, an RB1100 on v5.5 E.g.
NTP.png
your log says "ignoring received NTP Packet", but i don't receive any packet at all
i also tried a different ntp server (Debian, Source: ntp (1:4.2.6.p2+dfsg-1) Version: 1:4.2.6.p2+dfsg-1+b1) but same result:
06:38:32 ntp,debug,packet sending to 192.168.40.5 NTP packet (48 bytes)
06:38:32 ntp,debug,packet VN=4
06:38:32 ntp,debug,packet Mode=3 (Client)
06:38:32 ntp,debug,packet TransmitTimestamp=83aed068a970e6f2
06:38:32 ntp,debug Wait for 16 seconds before sending next message
06:38:48 ntp,debug Wait for 16 seconds before sending next message
06:39:04 ntp,debug,packet sending to 192.168.40.4 NTP packet (48 bytes)
06:39:04 ntp,debug,packet VN=4
06:39:04 ntp,debug,packet Mode=3 (Client)
06:39:04 ntp,debug,packet TransmitTimestamp=83aed088a7bc3c5b
06:39:04 ntp,debug Wait for 16 seconds before sending next message
06:39:20 ntp,debug Wait for 16 seconds before sending next message
06:39:36 ntp,debug,packet sending to 192.168.40.5 NTP packet (48 bytes)
06:39:36 ntp,debug,packet VN=4
06:39:36 ntp,debug,packet Mode=3 (Client)
06:39:36 ntp,debug,packet TransmitTimestamp=83aed0a8a7b99d45
06:39:36 ntp,debug Wait for 16 seconds before sending next message
06:39:52 ntp,debug Wait for 16 seconds before sending next message
06:40:08 ntp,debug,packet sending to 192.168.40.4 NTP packet (48 bytes)
06:40:08 ntp,debug,packet VN=4
06:40:08 ntp,debug,packet Mode=3 (Client)
06:40:08 ntp,debug,packet TransmitTimestamp=83aed0c8a7d5fdcd
06:40:08 ntp,debug Wait for 16 seconds before sending next message
06:40:24 ntp,debug Wait for 16 seconds before sending next message
06:40:40 ntp,debug,packet sending to 192.168.40.5 NTP packet (48 bytes)
06:40:40 ntp,debug,packet VN=4
06:40:40 ntp,debug,packet Mode=3 (Client)
06:40:40 ntp,debug,packet TransmitTimestamp=83aed0e8a9357603
06:40:40 ntp,debug Wait for 16 seconds before sending next message
06:40:56 ntp,debug Wait for 16 seconds before sending next message
06:41:12 ntp,debug,packet sending to 192.168.40.4 NTP packet (48 bytes)
06:41:12 ntp,debug,packet VN=4
06:41:12 ntp,debug,packet Mode=3 (Client)
06:41:12 ntp,debug,packet TransmitTimestamp=83aed108a7863bee
06:41:12 ntp,debug Wait for 16 seconds before sending next message
06:41:28 ntp,debug Wait for 16 seconds before sending next message
06:41:44 ntp,debug,packet sending to 192.168.40.5 NTP packet (48 bytes)
06:41:44 ntp,debug,packet VN=4
06:41:44 ntp,debug,packet Mode=3 (Client)
06:41:44 ntp,debug,packet TransmitTimestamp=83aed128a8476f2a
06:41:44 ntp,debug Wait for 16 seconds before sending next message
if i use 192.168.40.5 as dns-server
[root@sxt_bauer] /ip dns> print
servers: 192.168.40.5
allow-remote-requests: yes
max-udp-packet-size: 512
cache-size: 2048KiB
cache-max-ttl: 1w
cache-used: 9KiB
and query my SXT for an address, it's working. so udp communication between that hosts definitly works.