Effect of CFB IV reuse
It just leaks information about the blocks with the same IV.

Specifically, if the two messages encrypted with the same IV started with blocks $M_0$ and $M'_0$, then the attacker learns the value $M_0 \oplus M'_0$ (and if those where the same, then the attacker also learns the corresponding xor with the second block, etc)

However, the attacker learns nothing about the key, or about any message that wasn't encrypted with a shared IV.