hosting. nameservers partial unreachable

[A. Schulze]

Hello,

to day I noticed unreachable nameserver [a-d].nic.hosting. via IPv4
approved by at least two locations by such script:

for transport in tcp notcp; do
   for protocol in 4 6; do
     for host in a b c d; do
       printf "${host}.nic.hosting/${protocol}/${transport}:"
       if dig -${protocol} @${host}.nic.hosting. hosting. soa +timeout=1 +retry=1 +short +${transport} 2>/dev/null | grep --silent hostmaster.centralnic.net; then
         printf "ok\n";
       else
         printf "fail\n";
       fi
     done
   done
done

from AS31334 and AS15451:

a.nic.hosting/4/tcp:fail
b.nic.hosting/4/tcp:fail
c.nic.hosting/4/tcp:fail
d.nic.hosting/4/tcp:fail
a.nic.hosting/6/tcp:ok
b.nic.hosting/6/tcp:ok
c.nic.hosting/6/tcp:ok
d.nic.hosting/6/tcp:ok
a.nic.hosting/4/notcp:fail
b.nic.hosting/4/notcp:fail
c.nic.hosting/4/notcp:fail
d.nic.hosting/4/notcp:fail
a.nic.hosting/6/notcp:ok
b.nic.hosting/6/notcp:ok
c.nic.hosting/6/notcp:ok
d.nic.hosting/6/notcp:ok

from other locations I got 16x ok
Sometimes I also saw some OK for IPv4, too bit resolver so not retry as often.

Any hints?
Andreas