I do not know is it the appropriate place to report, but seemingly the following name servers are not answering at all:
2600:3c03::f03c:91ff:fe83:79dd (a.ntpns.org)
:
# dig +tcp 2.pool.ntp.org @2600:3c03::f03c:91ff:fe83:79dd
;; Connection to 2600:3c03::f03c:91ff:fe83:79dd#53(2600:3c03::f03c:91ff:fe83:79dd) for 2.pool.ntp.org failed: connection refused.
#
and
2600:3c00::f03c:91ff:fe8c:cf2c (e.ntpns.org)
:
# dig +tcp 2.pool.ntp.org @2600:3c00::f03c:91ff:fe8c:cf2c
;; Connection to 2600:3c00::f03c:91ff:fe8c:cf2c#53(2600:3c00::f03c:91ff:fe8c:cf2c) for 2.pool.ntp.org failed: connection refused.
#
With UDP, it just times out, so it looks like the name servers are not running.