I installed this mod along with the one I mentioned before, and after testing them for a while, I noticed that some of the mod’s slabs (mainly the wood and leaves) are not affected by the Additional Placements mod and are therefore only placed in their traditional form. While reviewing the files, I observed the following error message (the one sent is just one of the 32 blocks generating the error):

[Render thread/WARN] [Additional Placements/]: Generation type additionalplacements:slab cannot generate for new_slab_variants:oak_log_slab as it already contains the following properties that would be added:
[Render thread/WARN] [Additional Placements/]: [axis]
[Render thread/WARN] [Additional Placements/]: Add it to the blacklist inside additionalplacements-startup.toml to stop this message from appearing in the future.

Curiously, this does not happen with the leaves, only with the wood and all its variants in the mod.

For additional information, I am using version 1.20.1 and have installed the latest version of both mods released for this version of Minecraft.

This is not an error; it's intentional design to prevent the game from CRASHING if I attempt to add a property with the same name that another property the block already has. Regardless, I am going to start prefixing the property names with "ap_" to hopefully prevent this from happening again.

I would also like to add that I attempted to make this clear in the warning message generated, and it even tells you how to stop it from showing in the log again.

so it turns out slabs were already using "ap_axis" and not "axis" as the property name, but I never fixed the part of the code that prevents name conflicts. That's fixed now.