I'm on 1.20.1 Fabric

https://github.com/ChoiceTheorem/ChoiceTheorem-s-overhauled-village/blob/1.20/common/src/main/resources/data/ctov/worldgen/structure/small/village_beach.json

I replaced the "minecraft:jigsaw" to "lithostitched:jigsaw".
The structures in first pic is ctov:village/beach/jobsite/wizard_tower which injected by Lithostitched

lithostitched:jigsaw

minecraft:jigsaw

Disabled the injection and works. Have no idea of the reason.

Interesting after using "lithostitched:guaranteed" for injection.

With debugging. The lithostitched$structurePoolElements won't include the templates. There are only the injected pieces.
I found the reason here set it https://github.com/Apollounknowndev/lithostitched/blob/1.20.1/common/src/main/java/dev/worldgen/lithostitched/worldgen/modifier/AddTemplatePoolElementsModifier.java#L90
Is it intended? I think the original one should be iterated here instead of the elements()

It's fine :D

Fixed in 1.1.5.