Do you have a Google Play active in phone settings?

The only way to make sure your progress is saved regardless deleting the app or changing device, is to save your character in Google Play BEFORE deleting the app/changing.

To do so, go to More -> Settings in the old device and assign hero to Google Play.

If you see green text "already assigned" - it's done.

After that log on the same Google Play account on the new device and launch Questland.

You will be asked to load your old Hero from Google Play - you will see hero's nick and level.

Very important: make sure to pick the same server while signing in!