Hello,
First, I can confirm it works on a Pi3B (not +) as you expected ! Also, it seems to work fine with an amb loop on a large outside track.
After some testing at home with the decoder, I have a weird issue with an RC4 Hybrid that is not recognized. My setup is RTL-SDRv4, Pi3B, and a shitty loop with a 1:9 balun.
I tried a MRT and 2 RC4Hybrids, and one of the hybrid is entirely not detected. The two other transponder work fine, with occasional ghost transponders detected. I checked with my usual RCHourglass decoder and the problematic hybrid works fine, signal quality is identical to the other. I tried monitor mode : no frames. I tried increasing and decreasing the gain a bit, but no improvement. Same on PC. Only the ground noise increases in the status messages when the transponder is close to the loop (otherwise around -42)
Any idea ? Undetected transponder ID is 6215277, if that can help.

Thanks !
Jean