Many fans around the world have made their accounts by using Niantics trainer club website, which allows them to register without using their gmail.
The only problem with this is the trainer club logins seem to be going down very often while the gmail logins have no problem. It’s actually quite common to see some websites that host accounts like Niantic do to go down every once in a while. Most of the time it’s for maintenance and other times it’s from the maintenance.
We’re looking into reports that some Trainers are experiencing login issues. Thank you for your patience as we investigate.
— Niantic Support (@NianticHelp) July 14, 2017
As you see above Niantic has officially acknowledged the problem and is working on fixing it as soon as possible. Many fans are trying to prepare themselves for upcoming events, including legendary raids which could release legendary Pokémon all across the globe as a special feature trainers have been anticipating since the release of Pokémon GO.
It seems like the issue may have arrived when the previous update came around, though it also seems like it came once the migration hit though i’m sure the migration has nothing to do with it and everything to do with the recent update as most live games clients go down server wide after an update and require some tuning to make it work one again.
If you’re one of these fans, please be patient as they’re working on the fix now.