Complete All Abysses bugs - Cannot complete, last abyss doesn't spawn monsters

Bug Report ID: #1233128616

"Complete all abysses" bugs, sometimes the last abyss does not spawn the monsters, making it impossible to finish the abyss encounter.
Happened several times, this time we checked 0 monsters remains.
This still happening after the latest patches, this event happened 2025-12-22 around 21.45, GMT+1 Stockholm time.