There have been one or two mentions of a "bug" in doing the setting of leveling and trims, i.e., having to do it late in the 15-second window of opportunity following power up.
I have a thought
With my Spektrum gear, I power up the Tx and then power up the Rx. Sometimes, there is a rather long delay before the system synchs up. This can be several seconds, rather than the typical almost immediate synch that I am used to.
So, if I plan to do the Guardian initializing of trim and "level", I switch on the Tx with the Elevator held well off center. I then turn on the Rx and start to count to ... whatever.
As soon as I see the aircraft respond to my input - provided that I haven't counted to 15 yet - I do the Guardian initialization thing (toggle the Mode/Gear switch).
I don't need to bother with this whole procedure often, as I am not using 2D, my aircraft is trimmed to neutral Tx settings and Guardian has an excellent memory.
While I fully realize that there is no such thing as a guaranteed bug-free computer system, it is not unusual for us to interpret an unexpected yet natural behaviour as an issue.
As for "level" with a Guardian, I prefer to think of it as "known stable" condition. For example, when I first set up one of my planes with the unit, I had initialized it in the "level" attitude. When I tried Guardian, at altitude, the aircraft immediately recovered, with a decidedly nose-down attitude! Either adding or reducing power did not result in a desireable outcome; certainly, a novice could be rather shaken by this situation!
On this airplane, I initialized it with something over 10 degrees nose-up attitude. When I played with 2D recovery, it then stabilized into that slightly-above-stall-but-totally-stable attitude. Even had there been an engine failure, the plane could have landed well. At idle, it could have stayed up until the tank ran dry, even in windy conditions. With some application of power, it climbed nicely. In fact, I played around doing fully hands-off (Cat. 1) circuits, i.e., cut power to idle, leave the controls alone, add some power just prior to touchdown, let the plane touch, ramp up power and watch it climb out - "Look, Ma, no hands!". This can be done in 2D or 3D mode - you just get the right attitude (yours and that of your plane), and give it a go.
Guardian is amazing. It is simple to install and use. We make it complicated - that is our nature, we cannot help it!
Remember the old joke:
"Someday, and airplane will have only 2 creatures in the cockpit - a Man and a Dog. The Man is there to feed the Dog; the Dog is there to make sure the Man doesn't touch anything"
- Well, I thought it was funny, anyway ...