Possible Nameless Seer spawn bug?

Bug report reference number 2,07,35,98,403.
T16 Waste Pool Map, map mods in screenshot.
Mechanics in map -> Ritual, Harvest. 4 Scarabs used, Harvest Scarab, Harvest Scarab of Doubling, Ritual Scarab of Selectiveness, Ritual Scarab of Abundance.

0 monsters remaining. No side areas in map (Lab Trial, Vaal Side Area).
Harvest has been fully cleared. Ritual has been fully cleared.
Harvest area and Map boss room have both been checked for possible Seer spawn.
Character is currently standing in what I believe is the location of the final pack to die.
Build is RF Chief with Chieftain explode.