Loss of supervision refers to the heartbeat signal from alarm sensors letting the panel know they are present and functional.
My first recommendation would definitely not be to change out the panel, but it doesn’t look like this is related to a Surety subscription, so I am not sure what other reasons you might have been given for that recommendation.
Here is a general thread about supervision loss.
If you have used these sensors for a long time, battery may be the primary cause. Lower battery levels (with or without a low battery alert condition) can affect signal strength, especially if it is already a bit dodgy.
If the Edge is in a different location in the home than the GC2 was, some sensors may be out of range, or they may have more attenuation than before.