What are the problems with Diffie-Hellman groups 3 and 4 (RFC 2409 + RFC 2412)?
There is a relatively obscure attack, named the GHS attack after its authors Gaudry-Hess-Smart, that applies to binary curves where the exponent is not prime. In this case $155 = 5\cdot 31$ and $185 = 5\cdot 37$.

The main idea of the GHS attack is to map the discrete logarithm from an elliptic curve over, say,  $\mathbb{F}_{2^{155}}$ to a hyperelliptic curve of genus $16$ over $\mathbb{F}_{31}$.

Unlike elliptic curves, hyperelliptic curves of high enough genus have better-than-generic algorithms for computing discrete logarithms, and therefore the security of many curves over $\mathbb{F}_{2^{155}}$ and $\mathbb{F}_{2^{185}}$ is going to be smaller than you would expect from a proper strong curve. There are a few papers analyzing the $\mathbb{F}_{2^{155}}$ and $\mathbb{F}_{2^{185}}$ cases, and they largely conclude that such fields—that is, binary fields of composite degree—should not be used for elliptic curve cryptography.