I've got the same problem. Started all of a sudden, after years of use without an issue, with the camera not seeing the second battery (the one in the grip) occasionally. I would have to take the grip off and put it back on and it would - eventually - see the grip and the second battery.
Then it started doing exactly what Mike B described above.
I'm not sure if there is a connection/causality, but these symptoms started after I changed the regular strap for one connected to the tripod mount on the bottom of the grip (this one: https://www.adorama.com/br481005.html )...
Very disappointed... Especially since I read that X-T2 and X-T3 have issues with the battery grip (and without the battery grip the camera is not interesting at all..
