Gull + Beachhead - challenge not counted

Hello,
If this is not intended then this is a bug.
And I think it's a bug because the same strategy worked in Timeless Conflict.

As described above - tried using The Gull unique modifier for spawning Shrines inside Beachhead - that works fine, but upon killing the boss it did not count the kill towards the challenge - Divine Domination - and I had two shrines effecting me at the moment of the kill.

reference nubmer: 1,534,106,216