When you start exploring the possibilities of multi collection setups you start running into inconsistencies and errors.
e.g: say we have a footer configuration which has the option to create columns which in turn contain a bunch of links (pushing that one step further you could say that MenuLinkConfig contains another property for another hierarchical menu which again contains links)
after adding the footer config for the first time it seems at some point of adding configs you need to reload the entire editor app to be able to add the next item - it sometimes seems to forget what exactly it's editing and usually misses the collectionItemName in between the path. e.g. /menu/links instead of /menu/menu1/links.
Note: strangely enough a reload of the entire editor seems to momentarily fix the issue - this seems to suggest it's somewhere in the angular app which loses its footing at some point