This was the case on an android phone using Google login. His nexus 6X was on a beta build so he was unable to install the app. He started playing the game on an older device while he downgraded his 6X. After it was complete, he logged into his 6X using his google credentials and it prompted him to start over.
Probably because he was previously playing the Pokemon Go field test. All of the field test data was wiped, accounts and all. Everyone started over.
I've gone between three phones this week for various reasons, and this has not been an issue.
Not true at all. I've wiped the app from multiple devices and accounts today and it's always restored the player's progress after you log back in.
Seriously? What happens if I delete the app? Do I delete all of my progress?
I've yet to try that, but I can. I'll report back in a few. Having trouble logging into my iPod... will see if I can get my coworker to remove it from his older device.
Then you reinstall and all is fine. I went from using it on my Nexus 7 to my Nexus 5X and all of my progress was there.