The supplementaries fine wood slab does not have an additional placements variant.

You haven't supplied a game output log, so I don't know for sure, but most likely the block is supplying an "axis" property, preventing Additional Placements from adding it's own. I do plan to start appending "ap_" to the mod's property names from now on to help avoid this in the future.

This looks like the only item with this issue in this pack.

[26May2025 15:10:59.945] [Render thread/WARN] [Additional Placements/]: Generation type additionalplacements:slab cannot generate for supplementaries:fine_wood_slab as it already contains the following properties that would be added: 
[26May2025 15:10:59.945] [Render thread/WARN] [Additional Placements/]: [axis]
[26May2025 15:10:59.945] [Render thread/WARN] [Additional Placements/]: Add it to the blacklist inside additionalplacements-startup.toml to stop this message from appearing in the future.

You are not using 2.3.0. Please ensure you are using the latest version of the mod!

After updating it seems to work as intended.