AXFR stops working after a while in BIND9 9.16.

Summary

So, like with #1636, I noticed things not working any more, but this time, notifies were working, but it was axfr's that were not working any more.

BIND version used

(Paste the output of named -V.)

Steps to reproduce

Well, right now, it is "wait a few days".

What is the current bug behavior?

In BIND9 logs, I see:

Mar  5 07:46:33 ns3 named[73378]: client @0x28deb400 ipv4_address#57694: received notify for zone 'xxxx.yyy'
Mar  5 07:46:33 ns3 named[73378]: zone xxxx.yyy/IN: notify from ipv4_address#57694: serial 2020030336
Mar  5 07:46:33 ns3 named[73378]: zone xxxx.yyy/IN: Transfer started.
Mar  5 07:46:33 ns3 named[73378]: transfer of 'xxxx.yyy/IN' from ipv4_address#53: connected using 185.167.19.242#26276 TSIG yop
Mar  5 07:46:33 ns3 named[73378]: transfer of 'xxxx.yyy/IN' from ipv4_address#53: failed while receiving responses: connection reset
Mar  5 07:46:33 ns3 named[73378]: transfer of 'xxxx.yyy/IN' from ipv4_address#53: Transfer status: connection reset
Mar  5 07:46:33 ns3 named[73378]: transfer of 'xxxx.yyy/IN' from ipv4_address#53: Transfer completed: 0 messages, 0 records, 0 bytes, 0.007 secs (0 bytes/sec)
Mar  5 07:46:33 ns3 named[73378]: zone xxxx.yyy/IN: Transfer started.
Mar  5 07:46:33 ns3 named[73378]: transfer of 'xxxx.yyy/IN' from ipv4_address#53: connected using 185.167.19.242#23888 TSIG yop
Mar  5 07:46:33 ns3 named[73378]: transfer of 'xxxx.yyy/IN' from ipv4_address#53: failed while receiving responses: connection reset
Mar  5 07:46:33 ns3 named[73378]: transfer of 'xxxx.yyy/IN' from ipv4_address#53: Transfer status: connection reset
Mar  5 07:46:33 ns3 named[73378]: transfer of 'xxxx.yyy/IN' from ipv4_address#53: Transfer completed: 0 messages, 0 records, 0 bytes, 0.006 secs (0 bytes/sec)

Which I confirmed by using dig directly:

# dig -y hmac-sha256:yop:xxx axfr yyyy.yyy @ipv6_address
;; communications error to ipv6_address#53: connection reset

What is the expected correct behavior?

After restarting named on the master server:

Mar  5 08:03:13 ns3 named[73378]: client @0x28de9000 ipv4_address#50761: received notify for zone 'xxxx.yyy'
Mar  5 08:03:13 ns3 named[73378]: zone xxxx.yyy/IN: notify from ipv4_address#50761: serial 2020030337
Mar  5 08:03:13 ns3 named[73378]: transfer of 'xxxx.yyy/IN' from ipv4_address#53: connected using 185.167.19.242#60778 TSIG yop
Mar  5 08:03:13 ns3 named[73378]: transfer of 'xxxx.yyy/IN' from ipv4_address#53: Transfer status: success
Mar  5 08:03:13 ns3 named[73378]: transfer of 'xxxx.yyy/IN' from ipv4_address#53: Transfer completed: 1 messages, 116 records, 13597 bytes, 0.010 secs (1359700 bytes/sec)

# dig -y hmac-sha256:yop:zzzz axfr yyyy.yyy @ipv6_address

; <<>> DiG 9.16.0 <<>> -y hmac-sha256 axfr yyyy.yyy @ipv6_address
;; global options: +cmd
yyyy.yyy.          21600   IN      SOA     ns1.yyyy.yyy. root.yyyy.yyy. 2020030320 86400 3600 604800 1800
yyyy.yyy.          21600   IN      RRSIG   SOA 8 2 21600 20200324035558 20200303030727 43041 yyyy.yyy. KcunWHJt1kcskNuZKRBMfCmAInzjslmX4Sk3XVjPc2BVQkjkSvLljaNQ jfHU+LAN4Y+n2fcY3NWjRn05wG4Vp/ArGFuLH7LR8/sxMlSz3QlRLTce spBaZIZr8F3PGxXrfaQOKe9aBZImMypic0LnoMJD68nvu9cHzdFQVCtW FuM=
yyyy.yyy.          3600    IN      DNSKEY  256 3 8 AwEAAacp1eCSgm0KMB5khT6Ju7/BUBNtmOWYt6bJ1cI3mE91a42AuXuN jOniblRf5neJUlyaBFcVq+73UCyqtu/QW7qrVwgkTMiAcZhHh5WTvK50 ifPZCP01AfS1OgPK1EoSunBnFcZyr1h+3HJz5Ql9+IJR0qRDMCbBzx3O 0w+dPEV3...

Relevant configuration files

[snipped]

Relevant logs and/or screenshots

Pasted above.