Looking here, it does appear that the system is on an earlier firmware version of 2.6.2, which is prior to a critical update regarding cellular connectivity being released.
You can update your system either using Wi-Fi or an SD card. Steps to connect your panel to Wi-Fi can be found here.
You will need to update your firmware to version 2.6.3, then 2.7.2, and finally 2.8.1. Steps for each firmware version can be found below.
IQ Panel 2.6.3
IQ Panel 2.7.2
IQ Panel 2.8.1
Once the system is up to date, try running the cell test again to see if there is any change.