I put channel 8 on a switch to control the sonar while I test it. The sonar stays on regardless of the switch setting.
I was having similar problems, I found in my case if I toggled the Sonar switch on and then off before arming, it worked normally.
If I didn’t do that, it would randomly enable the sonar and stay that way (causing the lovely jumps in thrust that I can’t figure out over grass).
I’ll do more experiments with it.