This patch: https://gerrit.wikimedia.org/r/#/c/254107/ caused:
Error: Could not retrieve catalog from remote server: Error 400 on SERVER: Role class role::puppetmaster::frontend not found at /etc/puppet/manifests/site.pp:2116 on node palladium.eqiad.wmnet
So the puppet parser refuses to work correctly if you have an "import" that includes classes in a specific namespace, then you have some other classes from the same module/namespace but in autoload layout. This is only a problem it the classes in autoload layout are in the first-level directory, modules/$modulename/manifests/someclass.pp