[Bug, probably] "Compiling Shaders", over and over again, but only in 4.27.2

Since the project migrated from 4.26 to 4.27.2 the shader compiler keeps recompiling.
This happens during startup (splash screen) and then again when the editor opens, resulting in a slowdown until it finishes compiling 9000 shaders. However, I’m not touching any shaders and the project is 99% code.

LogShaderCompilers: Display: Started 10 'Local' shader compile jobs with 'Low' priority
LogShaderCompilers: Display: Worker (4/5): shaders left to compile 6262

DerivedDataCache remains empty.

Mostly solved, unclear how.