error sending response: would block

[Paul B. Henson]

I recently updated a couple servers that were running OpenBSD 6.3 with
bind 9.11.3 to OpenBSD 6.4 and bind 9.11.4pl2. Since then, I'm been
getting a large number of "error sending response: would block" log
messages:

Nov 15 11:03:58 lisa named[79587]: client @0x6f2f02bc440
10.128.30.77#65198 (p64-keyvalueservice.icloud.com): view internal:
error sending response: would block
Nov 15 11:07:42 lisa named[79587]: client @0x6f325b7a440
10.128.0.19#1851 (alt1.gmail-smtp-in.l.google.com): view internal: error
sending response: would block

I reviewed the article at https://kb.isc.org/docs/aa-00717 ; but it's
not clear - is this just a warning message, and it tries again and
successfully responds to the client, or is this a hard error and the
client never gets a response?

I wasn't getting any errors before the upgrade, and I don't think the
load on these servers is anywhere near high enough to cause them to be
overloaded.

Any thoughts on what might be going on?

Thanks...