Had the same issue. Talked to Uavionix about it. Here's what you have to do:
Assuming you've downloaded the Echo app and connect to your PING network, with your equipment powered up, go to Configuration mode on the app. Then...
Check all your config settings with data sheet from Uavionix based on your installed avionics.
Secret step: With TWO fingers touch the screen and hold for a few seconds. This opens up new advanced settings choices further down the screen. Look for Transponder Threshold setting.
You have to play around with this setting while flying until you can see consistent Press Alt readouts on the Monitor side of the app. Each time you put in a new threshold number, tap the Update Advanced button. Yes you have to go in and out of the two areas, giving your changes about 5 mins or so to see if they're working.
I had to lower my setting to 1100 before I got solid readings which was way below the number in Uavionix manuals for my equipment. It'll take some Avgas and some patience to get it working consistently!
Also, I took screen shots on my phone of every setting page, including the Advanced 'secret' page so I'd know how to restore if it went TU on me.