Update version 4 to 5 - same issue still persists. But I finally understand what were saying here.
For anyone who was unable to figure out why this happens. It's a matter of the default models being updated in 1.15. If you haven't edited any banner or shield entities you can fix the issue by doing the following:
Navigate to the 1.15 resources entity folder you extracted, it should resemble "1.15\assets\minecraft\textures\entity\banner" or "1.15\assets\minecraft\textures\entity\shield"
Copy all items in folder and paste them into your resource pack with the same folder structure. For example "Vicks-1.15-Textures\assets\minecraft\textures\entity\banner" or "Vicks-1.15-Textures\assets\minecraft\textures\entity\shield"
Ensure you overwrite all files.
Log in to Minecraft v1.15 if not already and load your resource pack. If you are already logged in "F3+T" will reload your pack.
Update version 4 to 5 - same issue still persists. But I finally understand what were saying here.
For anyone who was unable to figure out why this happens. It's a matter of the default models being updated in 1.15. If you haven't edited any banner or shield entities you can fix the issue by doing the following: