I am using a datapack on my server that adds a custom banner pattern. When I create a banner using the custom pattern via the /setblock or /data  command it functions correctly, but if I use pick block button (or /give command) to get the banner in item form, I am disconnected from the server with an exception message "Failed to decode packet 'serverbound/minecraft:set_creative_mode_slot''". In the server log the disconnect is indicated to have been caused by an IllegalArgumentException originating from the block.banner.CraftPatternType.minecraftToBukkit method.

It appears that the server is failing to convert the minecraft banner pattern into the Bukkit form. I have not had issues with other custom Datapack objects, like custom dimensions and custom enchantments, so I am not sure why this is causing an error.