I've had my Karma Grip/Hero 5 setup for a couple months now and have used it strenuously in all types of environments. I have not yet encountered an issue with the Grip not "talking" with the GoPro however I did find a review from an online blogger who had a similar issue:
"Sometimes the GoPro battery continues to drain after being turned off from the Karma Grip, which you won’t realise until the next time you try to power on the system and find the GoPro battery is flat. At first I thought there was an issue with the devices communicating with each other. Although the grip charges the cam, if the cam’s battery is completely drained it won’t power on again. Very bad, and here you actually need a spare battery for the cam, as there is no way to tell if the cam is “really” powered off."
I have not personally encountered the GoPro battery continuing to drain after I've turned it off from the Grip but if your GoPro is drained by the Grip all the way to power failure then it stands to reason you could perceive that problem as the devices not "talking" when the camera has actually died.
From what I can tell GoPro customer service has been very responsive after the drama with the Karma Drone so if you don't find your answer here that would be my next step.
Sorry for the over explanation, hope this helps and best of luck.