Finally hit rank 4 diplo to get my KDF Boff, and it won't let me claim it because I don't have enough room. The thing is, I just bought two boff slots specifically for the KDF Boff, and the 700 day Android. I can't claim him either. No room it claims.
Yet, if I try to activate any of the Boffs sitting on my ship, they'll join/train up as normal.