I'm having the same grey screen issues. The unit is fairly new (early Aug 2017) and the issue began about a week after purchase. I had come to this forum and found that I wasn't the only one with the issue and that an investigation was underway, so I decided I would just hang in there for a fix... and... still nothing. *sigh*
I did find covering a sensor helped, but it seemed to only double my playtime (to 30 minutes, maybe). I don't even try to play anymore... it's just not worth it.
Please let me know if there is anything I can do to expedite the process.