I've noticed that the original HKDF in rfc5869 defines a feedback loop. So the pseudo-code is something like:
for i = 1...n out[i] = HMAC(key, out[i - 1] + i + info)
However, the NIST recommendation 800-56C seems to only depend on a loop counter for each round:
for i = 1...n out[i] = HMAC(key, i + info)
From a security perspective, is there any significant weakness if we don't do the feedback loop?