I can't say why your phones have unstable GPS signals, if this happens all the time. If this is something that happens to you just sometimes, then I will have to say that it's normal.
My own ZenFone 6 has an accuracy of 3-4m which is perfectly normal for a phone. I have tried it next to other ASUS phones and competitors while walking around. Even though they all perform differently from time to time, they perform equally when putting all the results together.
The compass on all devices were also all inaccurate at some point and some even gut stuck which was easily fixed with a calibration in google maps. So it is just the technology as a whole. Some times you get great results, sometimes you do not. It is unfortunately normal if the compass is not accurate all the time but it should work most of the time and calibration is something you need to do quite often if you're trying to orient yourself while standing still.
Bottom line, a phone GPS is never as accurate as a dedicated GPS. Its main purpose is for navigation and not accurate measurements of a long run as these kind of measurements are never locked to the road (as when navigating). For this purpose, if high accuracy is of importance, you need to buy a professional GPS tracker.
If you suspect that your devices GPS is not working properly, then please compare it with other phones. You can always contact ASUS Service and ask them to test it if your ZenFone 6 wasn't performing nearly as well as the other phones you compared it with.
ZenBot
looks fine to me. i am from India. 
