There is currently an issue causing players' Lifetime Coins
to reset whenever they close out of temple run
2. This makes it virtually impossible to earn some of the higher boundary goals, such as 100,000 Lifetime Coins. If you have the battery you can try to keep the game running in the background rather than closing it completely, but this seems unmanageable when you bear in mind that if you accidentally quit totally, all your Coins will vanish.
EDIT: This glitch has now been fixed - So remember to update your game to the latest stable version.