'recursing clients' counter in stats is still underflowing on BIND 9.16.23-S1

As reported in Support ticket #19917

For example:

          4294445023 recursing clients

We seem to have addressed some causes of this anomaly in earlier versions of BIND (#1078, #1719 (closed)), but it is definitely still a problem.

There was one hypothesis that this might be related to DNS64 - however, no sign of DNS64 in this named.conf.

I would like to suggest that it might be due to one (or all) of:

• prefetch (it'd be easy to turn this off to confirm?)
• RPZ (yes, they have all of nsip-wait-recurse no and qname-wait-recurse no but whether or not additional recursion takes place is determined also by the actual policies in the policy zones themselves)
• Something awry with TCP socket handling?
• Something whacky with the interaction with serve-stale? (Although this is a default config., so stale-cache-enable yes;, stale-answer-enable no;.

No fetch-limits in this configuration, but if it was purely fetch-limits related, I think we'd have found and fixed it by now.