Thanks for headsup @NTPman ! The ipv6 servers should be fixed now. As for the dups, it looks like g.ntpns.org is running stale data, I’ll see with @ask how to fix that!
It looks like there is different kind of problem (timeout instead of connection reset) with another server 2001:41d0:700:335d::8:
tumbleweed:~ # dig pool.ntp.org @2001:41d0:700:335d::8
;; communications error to 2001:41d0:700:335d::8#53: timed out
;; communications error to 2001:41d0:700:335d::8#53: timed out
;; communications error to 2001:41d0:700:335d::8#53: timed out
; <<>> DiG 9.20.2 <<>> pool.ntp.org @2001:41d0:700:335d::8
;; global options: +cmd
;; no servers could be reached
tumbleweed:~ #
The server 2001:43f8:d60:300::201 has different kind of problem (routing?); it is mostly unreachable from North America. It is OK from the rest of the world, so it rather looks like routing issue.