The Bug:

Going off MCPE-184840 being reported and still open, I have noticed this in Java edition as well. Although the spiral staircase pitfall Encounter generates every now and again, the other Encounter types that create new rooms seem to be extraordinarily rare.

The changelogs made no mention of them seemingly meaning to be very very rare. In the past weeks of snapshots I’ve only found one encounter rooms  after visiting ay least 30 or so Trial Chambers in Creative.

Steps to recreate:

1. Open a few worlds, and locate several different Trial Chambers within them
2. Notice how, besides maybe the spiral stair spike trap, encounters more often than not just don’t generate at all