I have been editing a Collection, A collection by Thnidu: Contributions to watch, on my smartphone, in the Mobile Beta Frontend, with no difficulty. I go to "My Collections" (Special:Gather/by/Thnidu), make sure "My collections" is selected at the top of the page, click "Contributions to Watch", and click the Edit button.
But when I do the same in the Desktop Frontend, there's no Edit button or tab on Contributions to Watch. And when I hover the cursor over the "Special page" tab, the hovertext says "This is a special page which you cannot edit."
Helluva thing to call a collection.