While debugging T383710 I tried to reproduce the issue locally.
As expected we don't have the network limitations as in k8s environment but I encountered another issue. More specifically:

When I tried to GET this snapshot with the overlay map

• GET http://127.0.0.1:6533/img/osm-intl,9,-5.098,145.55,280x280.png?lang=de&domain=de.wikipedia.org&title=Gogol_River&revid=236236557&groups=_e189b45ad898f56f2d6b7e3a359fedaf5daef408

Kartotherian returned this error

failed to initialize projection with: '+init=epsg:3857' in Map

Turns out the root cause is in one of the mapnik dependencies. More specifically:

• We use geojson-mapnikify to convert a geojson to a mapnik map.
• This library uses an xml template to wrap the geojson to the mapnik XML input.
  • https://github.com/johngian/geojson-mapnikify/blob/master/lib/template.xml
• It defined the projection to be used with the +init prefix which is deprecated in our current libproj-dev version.