Detecting GPS signal loss in OpenIMU300ZI with uBlox

Hello,
Is there any way to detect the GPS loss from OpenIMU output data? I'm using OpenIMU on a route which crosses an area with GPS jamming.

The firmware application is "INS Application", version "OpenIMU300ZI INS 1.1.1"

When entering the jamming area, a 3rd party GPS analyzer shows that no satellites are available, and the GPS location received from OpenIMU starts experiencing substantial drift, but no indication is given that the GPS signal was lost.

I retrieve data from "e2" payload, and the value of opMode is 4 (as normal).

Thanks!