I've noticed some problems with the vanity paths register in AEM6. Please take a look into the Resource Resolver status page in OSGi console: /system/console/jcrresolver and try to find the mapping that have been created based on your vanityPath. For a simple /mypath it should be sth similar to ^[^/]+/[^/]+/mypath(\..*).
If you won't find the mapping try touching the node through the CRXDE. Just add a random character at the end of the `sling:vanityPath` property, save the node and the rollback to the original value. Afterwards check if the mapping registry has been updated.