First Steps
Here are the initial steps to try:
Turn the phone off/on
Turn GPS off/on
Disable any battery saver settings, including Power Saving Mode, Battery Management, or any third-party apps
Perform an AGPS reset (Install the App GPS Status & Toolbox, in that app, go to Menu > Tools > Manage A-GPS State > Reset)
Adjusting Battery Saver Settings on Different Devices
HTC: Access your phone settings > Battery > Power saving mode > Battery optimization > Select your app > Don't optimize > Save
Huawei: Turn Energy Settings to Normal and add your app to Protected Apps
LG (If you're running Android 6 or higher): Settings > Battery & power saving > Battery usage > Ignore optimizations > Turn ON for your app
Motorola (If you're running Android 6 or higher): Battery > Select the menu in the upper right-hand corner > battery optimization > Not optimized > All apps > Select your app > Don't optimize
OnePlus (using OxygenOS Settings): Battery > battery optimization > switch to all apps > select your app > Dont optimize
Samsung: Access battery settings > App power saving > Details > Your app > Disabled
Sony (If you're running Android 6 or higher): Battery > from the menu in the upper right-hand corner > Battery optimization > Apps > Your app
Xiaomi (MIUI OS) If you're running Android 6 or higher: Access your phone settings > Additional settings > Battery and performance > Manage battery usage > Apps > Your app