[2021] Pantheon Upgrade (Soul of the Brine King) Oversight

Since i learned it the hard way today, i wanted to give you guys a heads-up.

If you want to upgrade "Soul of the Brine King" the first time for the 30% inc. Stun and Block Recovery, you have to kill Otesha, The Giantslayer.
This Mob is found in the Iceberg-Map, all fine. Until i got nothing back after finishing the map.
As stated in the Wiki, there are 3 possible Bosses.
So you have a 1/3 chance to get the upgrade, else you waste a map and a vessel.

This is super annoying and i still didn't get my upgrade =(