If your code using C3 Runtime and as long as device not supported webgl by default in their browser will face this problem. Although the phone fullfill the basic requirement (5.0+ Lolipop)
Use "Remote Preview" in the project, copy the url link to default browser (NOT chrome/firefox) in your android phone, then this "browser not supported" will appear. Most of android phone only have default browser which is not supporting webgl, it need additional browser Chrome/Firefox installed from Google PlayStore.
It will run normally if you run the "Remote Preview" using chrome/firefox in the same phone which has problem "browser not supported"
If you are using C2 Runtime, probably will run normal or a black screen come out instead of "browser not supported" that means some plugins (such as MobileAdvert) not supported by the phone browser.