Hello
So before I came to Japan, I transferred my American phone number to Google Voice.
The phone # came from a family plan that my family in the US still uses, but I was removed from the plan. I can still use the phone number.
Anyway, when accessing different websites that I used 2FA with my phone number (now on Google Voice) 50% of the time the 2FA text message arrives, and 50% of the time it doesn't
Why does this happen? Is it because the phone number is no longer associated with a phone plan? Is there a way to ensure that my US phone number (on Google Voice) always receives the 2FA texts 100% of the time?
If not, is there a method to get a new American phone number and use that (on Google Voice or something) to ensure 2FA text messages always work?

Thanks for the tips