Config.yml

IAWAILA has a config containing settings that may be of use for you.
This page explains them.

ignored_blocks

Type: List (String)

This option defines blocks that should be ignored when IAWAILA generates the Font file for the block images.
It is recommended to not remove the default values, as it could otherwise cause loading issues for the client, which ends up in the font not being loaded.

Supported options are Vanilla blocks, ItemsAdder Blocks and Furniture using the <namespace>:<id> format.
As an example, if you want to ignore barries can you add minecraft:barrier to the list.

block_overrides

Type: Map (String, String)

By default is IAWAILA looking for textures in plugins/ItemsAdder/contents/waila/assets/waila/textures/block/<namespace>/ to be added to the font file. If no file is found will it check if the Block in question is a Minecraft block and if so defaults to using minecraft:block/<id> as texture path.
This behaviour can work for most, but not all blocks, as some may have a different name or not even a proper texture.

This is where this config option comes into play.
Each entry in this option consists of the block's Namespaced ID (<namespace>:<id>) as key and the texture that should actually be used as value.
You shouldn't be required to touch this option at all and only do so if you understand how referencing textures works, as it could otherwise cause broken image paths resulting in the client refusing the font, displaying it as squares.