X_REFERENCE_APP_UNREFERENCED
Means
a tracked app typechecks but the root tsconfig.json does not reference it
Typical cause
the app came off the typecheck pin without joining the root tsc -b solution, so the packages' emitted .d.ts are never proved consumable
Fix
add { "path": "./<the app>" } to the references array in tsconfig.json — fix carries the exact entry