Core's Special:EditWatchlist has now switched to a table layout and has a new label-assigning feature. This works on small screens fine, for responsive skins. However, MobileFrontend has a completely different Special:EditWatchlist, and so the new feature isn't available when that extension is in use. Either MobileFrontend should be updated to use the core special page (which is T266065) or to have the new watchlist labels features.