Boss Annihilator Triumph - Court of Blades Bosses question

So this is the last triumph I have left, and seems I keep getting dread/taken bosses every time.

I assume this is random, but will ask anyways.

Besides doing expert on Hive weeks (like this week), is there a schedule/rotation for hive on normal?

I did a bunch of dread/taken bosses yesterday, so was hoping today would be hive day, but nope, same dudes again.

I have gotten 1 hive encounter in my last 15 or so.

Am I just that unlucky or am I playing at wrong time?