RHEL/CentOS/OEL clients, Package Upgrade jobs in SUMA never complete

We have a mix of SLES, RHEL, CentOS and a few OEL servers as managed clients (all salt) in our SUMA environment (4.1.8 server and proxies). We have noticed that very often if we apply software updates from our CLM-cloned channels to non-SLES clients (RHEL, OEL and CentOS) then the “Package Install/Upgrade” jobs in the Schedule still shows those machines as Pending, even though the yum/dnf jobs on the machines have completed and all patches have been applied. Upgrading available packages in the same way to SLES systems seems to work fine, at least in most cases. The non-SLES machines will do this regardless of whether or not there are salt/salt-minion packages in the list for updates.

In the salt minion logs on affected machines we see a lot of messages like this:
2021-07-21 18:22:35,886 [salt.loaded.int.grains.core ][ERROR ][2561] Exception during resolving address: [Errno 1] Unknown host

It doesn’t suggest what host it’s trying and failing to resolve though. I can’t see anything in any of the files in /etc/salt/ which mention any unresolvable hostname, the only host mentioned in there is the proxy or SUMA server they are registered to which is resolvable.

Anyone else seen this and got any pointers?