Odd. Try long pressing it, open app info, tap syorage, and tap clear storage

Sorry for the delay in response. I've heard occurrences of this happening and the reasoning could be that either

• the data is being synced back up from a backup, or
• Thunder is saving its local database somewhere on your device which does not get cleared properly

For now, the temporary fix if you encounter this issue is to go to Debug -> Clear Local Database, and that should completely remove any local data from your device!

Do you have app backup/syncing enabled with Google? I've had some oddities occur from my phone automatically pulling old app data for Thunder from a previous sync.