@MaxGyver I believe I have identified the cause of these errors. If I am right, they only occur when the input shaping frequency is below about 12Hz, which would explain why nobody else has reported Code 3 errors since we released beta4.
Please try the new 3.6.0-rc.2+2 main board firmware binary from https://www.dropbox.com/scl/fo/nlkfneaas1osgtdw37s17/AIS_H0KSAKCmfYSjSRTSOAE?rlkey=ad4omnq36zkdz3wl8i7kthqqt&dl=0. You may keep your expansion board binaries at 3.6.0-rc.2 or upgrade them to rc.2+1 from https://www.dropbox.com/scl/fo/kj7gwwzxg5lhe26twph5z/AAdwkPCTYi6bcogLmIIIup4?rlkey=8oo6z5il7wzk2u5b7qpykf3qv&dl=0.