Steps to take depend on a few things like the panel model and firmware version. On IQ Panel 4 and IQ Panel 2 there are a couple known issues causing trouble for the cell radio to connect, issues which were resolved in firmware updates. The first thing to check on the IQ Panel 2 or IQ Panel 4 is the firmware version to see if it is up to date with the latest. I am linking guides at the bottom.
If that is not applicable, a panel power down is the first step to try. Do the power down instead of the standard reboot so that you can leave the panel powered off for 2+ minutes before rebooting.
Settings > Advanced Settings > Power Down.
On your connected system (IQ Panel 2) it looks like your firmware is up to date and your panel is responding to cell pings. Did you resolve this issue with troubleshooting already?