Quick answer: Godot 4 ResourceLoader given a relative path failing to load from PCK? PCK content uses absolute res:// paths; convert before lookup.
load("icon.png") fails; load("res://icon.png") works. Code that builds paths relatively fails.
Always use res://
Prefix all asset paths. Loader resolves consistently.
Or normalize at boundary
If callers pass relative, wrap in res://. Code is defensive.
Audit path-using code
Each load call's path source. Inconsistent prefixes surface; fix systematically.
“Paths in Godot are URI-style. res:// is the protocol.”
Establish the convention: 'always res:// prefix' in your project. Lints can enforce; consistency follows.