As far as I know, the shader cache gets invalidated and deleted whenever a Dolphin version have changes in its shader system. It's similar to save states, there's a variable somewhere in the code that whenever it gets incremented the shader cache the user already have gets invalidated...
Avell A70 MOB: Core i7-11800H, GeForce RTX 3060, 32 GB DDR4-3200, Windows 11 (Insider Preview)
ASRock Z97M OC Formula: Pentium G3258, GeForce GT 440, 16 GB DDR3-1600, Windows 10 (22H2)
ASRock Z97M OC Formula: Pentium G3258, GeForce GT 440, 16 GB DDR3-1600, Windows 10 (22H2)