There are a few different GNSS modes that can be selected from the GNSS chip. It is recommended you select the one that meets your application, otherwise, the GNSS may not work properly and the device will not able to lock with the GNSS signal. 

Please make sure the firmware is updated to at least version ThinkRF R5700/R5750 Firmware v1.1.5. The latest version to date is ThinkRF R5700/R5750 Firmware v1.1.6

More details can be found in GNSS Commands from ThinkRF R5700/R5750 Programmer's Guide

Here is a quick step to step on how to set up GNSS mode by using Telnet through PuTTY.

Use the WSA discovery tool or ThinkRF S240v5 v5.1.3 Real-Time Spectrum Analysis Software to find out the IP address of your RTSA.

Connect PuTTY to both ports 37000 and 37001.

Once it's connected, check the connection by using *idn?, and then check the existing GNSS mode setting by <:GNSS:DYN:MODE?>

Set the preferred mode (Mode 4 in this example) by <GNSS:DYN:MODE 4>

Verify the mode by using <:GNSS:DYN:MODE?>

The R5750 and R5700 will retain the user's last entered mode selection value through power cycles.