r99: Seahorse patriarch doesn't seem to drop cloak anymore
 

I've killed him at least 20 times now, not a single cloak. Used to be 1 cloak in 2 or 3 kills.

RNG.

I have gone 15+ patriarchs with wizard rods a few times. Same on matriarch.

A few weeks ago I had a cloak drop my first kill when I was really after a wand.

Assuming a 20% cloak drop rate, the probability of having no cloaks drop after 20 kills is a little over 1%(~.0115).

Looks like you hit the unlucky jackpot. Random numbers are random.