Expected:

Trials chambers should generate regardless of being partially generated due to previously loaded chunks from previous versions. 

Observed Results:

Trial chambers partially cut off in any way from previous versions will fail to generate completely.

Steps To Reproduce Roof:

1. Start a Minecraft world in a version before 1.18 (preferably 1.17)
2. Teleport to a location where know where a trial chamber is
3. Exit the game and load the world in 1.21
4. Go into spectator mode to see the observed results.