The roslyn repo contains prebuilts as identified by the prebuilt report at artifacts\prebuilt-report\annotated-usage.xml in the Offline BuildLogs for any installer build. These prebuilts need to be resolved by either a) conditioning out the code that includes the package, b) updating the package version to use the version that is built in source-build (using package version flow) or c) adding the package to SBRP.