SRP-6 vulnerabilities when N is small
Solving a 256-bit discrete log is absolutely doable, and quite quickly, these days; there are public tools that can do it, though they may require some expertise to use. 

On that note, even a 1024-bit modulus is not particularly conservative: it is generally agreed that well-funded organizations today could break logs of that size as well, but at a very large cost. The current minimum recommended modulus size for RSA, Diffie-Hellman, SRP, etc is 2048 bits.

That being said, I would also put my money on a client or server-side break-in before arriving at the conclusion that the log was being broken.