Hey,
Are you using a Dockerfile based app? If so, does your base image use Alpine Linux? Only if so, I’ve previously had similar weird errors with DNS when running a Node app. Couldn’t figure it out either! What fixed it for me was switching to a different base image, such as XX-slim. And then the DNS errors went away. Total guess but can’t hurt to try.
e.g
https://christoph.luppri.ch/fixing-dns-resolution-for-ruby-on-alpine-linux