DNS under docker swarm failing randomly

I have a docker swarm, running on CentOS 8.3.2011, version 20.10.8.
I have the swarm across 3 servers, with a bunch of stacks sharing the same network.
While things seems to work, from time to time services fail with problems resolving DNS.

I have no idea how to debug this issue.
I am happy to share bunches of my stack configurations, but also not sure what is relevant to share in this case.

Thank you for any insight on this problem.