Quick answer: GameMaker shader changes not visible in YYC builds? Shader recompile is incremental and sometimes skipped - run a clean rebuild after shader edits.
Edited a shader; YYC build still uses the cached previous version.
Clean and rebuild
Build > Clean > Rebuild. Cache invalidates.
Or touch the project file
Save the project after a shader edit. Forces dependency re-evaluation.
Pin shader version
Shader includes a constant string 'v3'. Modify on each edit; cache invalidates by content.
“Build cache hashes content. If content didn't visibly change, cache assumes nothing did.”
If you edit shaders frequently, the clean-rebuild habit is mandatory. Cache-bust is the only reliable workflow.