This might be a FW5.3 issue and not a D75 issue. Does what this guy just posted sound familiar?
Interestingly, I had pretty much the exact same issue when i tried FW5.2 on my trampa VESC6’s. Detection results were consistently terrible, and the only solution was to roll back to FW5.1. I’ve also heard of plenty of other folks having detection issues on FW5.2, and now FW5.3. Seems like a total coin flip whether someone will get decent detection results with newer firmware.