I'm a very new resource pack designer. I'm making a PVP pack just for myself and a few of my friends to use privately. The thing is, I'm really beginner, and I don't want to make a pack entirely from scratch, so I took "Faithful 1.12" resource pack and am just editing the textures I want to change (lower fire, transparent gui, etc).
When I load my pack into Minecraft some of my textures don't work, they just show up as vanilla. I've double and triple checked everything, it's all properly named and in the right folder. The weird thing is that it's only about 1 in 10 of my textures that do this. (I am playing in 1.12.2 and using Paint.net to edit textures)
Check to make sure that your .PNG files have a 1:1 aspect ratio for normal textures, or a 1:x ratio for animated textures where x is the number of frames in your animation.
If you're absolutely certain that the textures are in the right place, the right format and the right aspect ratio, check your log file to see if there are any errors when you start up or refresh resource packs.