Trial of the Sekhamas Test of Will - Hourglass trials

Some hourglass trial maps have only 2 spawning points (indicated by dormant Urnwalkers) for Rare enemies.
These maps either do not spawn Rare enemies at all, or they just stop spawning at some point. My guess is that when the game tries to spawn a rare from the non-existent spawning point, it just stops spawning rares alltogether.