Battery.
I've been able to use the fob while fairly far from the car, however, summon never worked from the same distance. Since they list 10 feet for summon, it has to be a safety factor in the event the fob fails for some reason to halt summon, and 10 feet or less away would be within range to tap a door handle to halt it.
No doubt they judge distance by fob signal strength, so that too will fade with a weak battery.
Could be something unrelated, but my bet is battery...