By just having a tracker in phone does not guarantee that it can be tracked from anywhere at any time. Multiple factors play important role in phone tracking, below are explained detailed reasons due to which you cannot track your phone:
It is possibility that you lost your phone in some environment in which it got damaged (Dropped in water, dropped on road, left on some humid place etc.) due to which it is unable to connect with network.
Tracking was off:
Another solid reason due to which phone cannot be tracked is that its tracking is off or mobile data is turned off. Many people turn off phone tracking apps because it uses GPS and Mobile Data connection which drains battery and costs a lot. Some people turn off tracking because of privacy issues.
Weak Network Connection:
Weak or limited network connection is another reason that you are unable to track your phone. Phone tracking is performed through nearest cellular phone network tower which uses GPS to provide details about exact location of phone, if phone is in an area where signals are low and connectivity issue is common then phone tracking does not work.
Bad weather can disturb network connectivity. It weakens the signals and such poor signals are not capable of tracking the mobile phone. Therefore, if there is heavy rain, dark clouds or some thunderstorm then there are chances that your phone cannot be tracked.
Phone is powered Off:
A SIM card cannot be tracked when it is off. Because tracking a phone requires SIM card to connect with nearest network provider’s tower. In case when SIM is not connected with tower, GPS does not work and phone cannot be tracked.
Phone Tracking Application got accidently flashed:
It is also a possibility that your phone tracking app got crash or flashed away due to virus or some potentially harmful software. Unavailability only leaves phone with network connection and if whole OS of your phone is attacked or infected by virus then there is no way to track your cell phone.