Here's what I did:
1. Using LDPlayer9.
2. Using an unsigned mod.
3. Having save data already in Google Play Games.
4. Completely deleting the original application.
5. Performing a fresh installation from Google Play.
6. Loading the game to 100%.
7. Clearing stages 1-10.
8. Loading past data on the account linking screen.
That's all.
To Professor
@bedo:
If signing is difficult, how about making it "LOOT exclusive"?