All modern mobile operating systems centrally select the most power efficient method of determining the phone’s position from the different location providers available (GPS, Wi-Fi, cell towers). Depending on your version of Android, you have different options to verify that the power-efficient methods that use Wi-Fi scanning are enabled:
In Android 5.0 to 5.1.1 you can go to Settings/Wi-Fi and open the advanced options (mostly they are located in a submenu with 3 dots in one of the corners). Here make sure that “Scanning always available” is enabled.
In Android 6 and higher you can go to Settings/Location and open the Scanning menu (mostly in a submenu with 3 dots located in one of the corners). Here make sure that “Wi-Fi-Scanning” is enabled.