In my case, it's not the GoPro firmware version that is causing a problem. I have checked for an update (again today), and there is none, mine is up to date. I was having connect issues when I first received my Solo three weeks ago. I did the GoPro Firmware update then and it worked perfectly for two weeks. As of this week when I did the Solo firmware update (App / Solo remote), it definitely indicated the (Solo App) update would improve video transmission (I am assuming between the Solo and the handheld transmitter). This is surely not the case (at least not with my equipment, Hero 4 Black and Samsung Galaxy 5S). Something has changed (and not for the better) for the Video WiFi packet TX/RX.
In my opinion, it is between the Solo and the handheld TX because video works fine out to about 150', after that, black screen and video lock-up. It would be nice to be able to revert to the previous version. Though stopping video record when you land / power-down the props is a nice feature, it sucks not having video for flight.