BEFORE POSTING A BUG REPORT, PLEASE ENSURE THAT IT IS A UNIQUE BUG AND NOT A COPY OF ANOTHER OPEN ISSUE.
IF THERE IS AN IDENTICAL OPEN ISSUE, PLEASE ADD YOUR INPUT AS A COMMENT TO THAT ONE.
IF YOU ARE UNSURE IF THE ISSUE IS IDENTICAL, ASSUME IT IS NOT.

Include the following at the top of your report:
Minecraft version
1.21.1
Mod Loader (please include the version!)
NeoForge 21.1.196
Mod version
v2.3.1
Any other mods you are using. Include the versions. A pastebin or equivalent link is recommended if you have more than 3 additional mods.
Double Slabs v0.2.3

Describe the bug
When placing slabs vertically, you cannot mix two different slabs (Slab A and Slab B) as the Double Slabs mod allows directly, instead you must place a temporary vertical slab (any slab except Slab A or B would work), then try to place Slab A vertically against the temporary vertical slab. This will place Slab A vertically one block over. Then, still against the temporary vertical slab, try to place Slab B vertically. This will place Slab B in the same block as Slab A, both vertically. However, the top and bottom faces of either Slab A, or else Slab B (but thankfully not both) will not render.

To Reproduce
Steps to reproduce the behavior:

1. Place Slab A vertically.
2. Attempt to place Slab B vertically against Slab A.
3. Attempt to place Slab C vertically against Slab A.
4. See resulting visual and block placement error...

Expected behavior
One should be able to place different types of slabs vertically against each other, just as one can do horizontally when Double Slabs is installed, and all faces of the mixed double slabs should render.

Screenshots

Additional context
None.

Please upload the crashlog (if applicable) or game output log (latest.log in the logs folder, not the log from your launcher!). Additional logs may need to be added upon request.
latest.log