These Settings must be properly configured to keep CellTracker working.
1) Settings => Battery => Battery optimization => « GPS » => Don’t optimize => Done
2) Settings => Battery => Battery Saver & Adaptive Battery => Turn OFF
3) Settings => System => Recent app management => Normal clear
4) Settings => Apps & notifications => See all apps => « GPS » => Data usage => Backgroud Data & Unrestriced data usage => Turn ON