Custom jigsaw fallback structures fail to generate

When making a custom jigsaw structure, one of the fallback structures fails about half the time and two of the other fallback structures fail 100% of the time. There are no errors or warnings in the logs when generating.

Steps to recreate:

1. Download and apply provided datapack in a 1.21.11 world.

2. Place a horizontal jigsaw block with “kirby:amethyst_keep” as the target pool, “kirby:cavern_keep” as the target name, with the levels set to at least 10 and jigsaws turned on. (I haven’t tested with lower number levels).

3. Generate and notice where there are dead end jigsaw blocks.

In the picture with the circles, the blue circle is where a fallback structure generates some of the time while the red circles are where fallback structures never generate. The picture without the circles is what it should be. (I placed the missing structures manually).