If fpcalc encounters a decoding error for which it still was able to generate a result it will return the special return code 3. See https://github.com/acoustid/chromaprint/blob/master/src/cmd/fpcalc.cpp#L403-L408 and acoustid/chromaprint@3f07cee

In such cases Picard should continue doing the lookup to find matches instead of failing completely. It probably should however not store the fingerprint for submission.