Looking at https://grafana.wikimedia.org/dashboard/db/resourceloader we've got a really low rate of error responses.
5xx is 0 for days/weeks at a time. Only exception to this I found was during MW problems/outages not related to RL.
4xx is non-zero, every few minutes a few pop up here and there. This is fine, but it I couldn't quite understand why or what would cause them, given I know of no code in RL that would issue such a response.