Updated from version for MC 1.19.4 to 1.20.1 and this happened.
Flags now are corrupted and do not show up on a plane correctly(

Most likely fixed in 0.7.4, if not please respond here

Unfortunately, still not rendering right on 1.20.1 with 0.7.5. Seems as though it only renders the first layer the banner has on it-- not all of them.

Interestingly, I can not reconstruct this issue myself.

To make sure we have the exactly same setup, can you try this banner here via give command: https://minecraft.tools/en/banner.php?color_id_0=11&shape_id_1=22&color_id_1=2&shape_id_2=33&color_id_2=12&shape_id_3=26&color_id_3=0&shape_id_4=7&color_id_4=0&shape_id_5=8&color_id_5=0&shape_id_6=36&color_id_6=0#crafting

Also, can you try without shaders in case that breaks.

Ran it again with your flag code; minus the shader and the resource pack for Create texturing; same issue. Gonna try it again without AdditionalBanners in this modpack, that's the only other thing I could think of that might be meddling with things.

UPDATE:

That's without Additional Banners in the pack; which is... Vaguely disappointing. Doesn't throw a fit with shaders, either; which means it was a problem on my end, apologies for the wasted time. Is there a method that could be wrangled for compatibility with custom banner additions like a datapack setup that I don't know about, or are those two just... Destined enemies?

We are having the issue as well with our pack https://www.curseforge.com/minecraft/modpacks/cstmgames-creative-tendencies

we are also not using any banner modification mods / datapacks.