Looks like we have another Nicalis-published title that has vanished into thin air.
A nasty situation surrounding Ittle Dew 2 recently came to an end a few weeks back, which finally saw the game make its way back to the Switch eShop without Nicalis as the publisher. Now we see that Cave Story+, another Nicalis-published game, has disappeared in the United States.
The game remains for sale in Europe and Canada, but there's no word on what's going on with the U.S. in particular. Along with that, the game's official page on Nintendo.com has had all of its info yanked, and it doesn't even come up if you search for it within Nintendo's own site. Hopefully we get some statement on the matter in the near future.
UPDATE - The issue with the listing has been resolved.