It used to show a zoomed in glitch banner, before it was not visible.

Hi! Can you test without any other mod as well as with this specific banner please:

/give @p minecraft:yellow_banner{BlockEntityTag:{Patterns:[{Color:13,Pattern:"mr"},{Color:3,Pattern:"moj"},{Color:15,Pattern:"bo"},{Color:15,Pattern:"bs"},{Color:15,Pattern:"ts"},{Color:15,Pattern:"gru"}]}}

Let's also merge with #125

Based on how many people find this issue its probably something fundamental, yet I can not reproduce this myself.

Using this mod pack https://www.curseforge.com/minecraft/modpacks/cstmgames-creative-tendencies