@IPeak@Chu Sounds like the update was corrupted along the way or your Switch's internet settings are awry. If you play within the house, are you able to start the game just fine?
Yes, the games play just fine. Have no problems with any of the internet functions like max raids or the mystery gifts. I just get that frase first thing before the game loads. How do you know if the expansion pack content is corrupted? And is there any way to fix it?
From Greninja's popularity. Though there is the possibility of Greninja never showing up ever again, Greninja's just too popular for them to shelve permanently, between it being in both the Super Smash Bros. games and the
Detective Pikachu movie.
No, Gyarados can appear in the common dens as well. I got my Moxie Gyarados off of a common den.
If you have trouble finding them, and you can go online, I suggest you do so. Gyarados raids pop up ever now and then.