Missing cookie

[J Doe]

Hi list,

I run a validating recursive resolver with BIND 9.18.27.  Over the
course of many days, I have noted the following warning about a missing
cookie from a particular server:

     09-May-2024 20:09:22.277 resolver: info: missing expected cookie
         from 192.5.5.241#53

This server runs in the cloud with excellent connectivity, I don't do
anything special with my firewall and I do not run any software that
would mutate the DNS data over port 53.

What could be causing the cookie to not be received from this particular
server over a number of days ?

Thanks,

- J