When a collection has collaborators the collection is listed in each collaborator's profile but once the the collection is made private it's no longer visible for owner of the collection:

https://musicbrainz.org/user/<editor name>/collections

Due to lack of subscriber on my private collections I couldn't test if this also affects the subscription page for other users:

https://musicbrainz.org/user/<editor name>/subscriptions/collection

When viewing my own subscriptions it says correctly I'm subscribed to " <number> private collections" but doesn't actually list when I'm the owner of them.