I have just solved a little mystery with my GMG Davy Crockett grill, that has puzzled me for months. I really do like my grill, but this issue was the one nagging thing that annoyed me. This may be old news to those of you with GMG grills, but I'll post, just in case it helps someone.
The grill's WiFi can operate either as a standalone access point (i.e. you connect your phone or tablet directly to the grill) or in network mode, where the grill connects to your own WiFi network, and can be accessed that way.
What I found was that in network mode, I could connect my phone or tablet to the grill *if* I connected directly via the same WiFi access point, in the garden; but not if I was connected to my main access point in the house. This is despite them being on the same network, and everything else working (i.e. my phone, in the garden, can access my NAS in my office, etc). This has been bugging me for ages, especially as the whole point of going WiFi was so I could monitor my grill during the day, while working.
I figured it had to be something to do with my setup, and I even replaced the access point in the garden, but to no avail. What confused me more was that sometimes, connecting in the garden, but then going back into the house (and on the house WiFi), maintained a connection to the grill, but the moment something happened to drop that, I could no longer connect again, unless I went back out into the garden.
Turns out that it is the GMG app's programming. When the app is launched and asked to connect, it notes the SSID that the phone/tablet is connected via, and only looks for GMG grills connected to that SSID. I had given my garden WiF access point a different SSID to the main one in the house. Once I renamed it to the same SSID, everything worked, and I now have a solid connection from my office in the front of my house, to the BBQ area behind my garage, in the back.