A portal no longer rebuilds a module it does not sync — it tells you

Modules arrive on your portal as prebuilt bundles. When a bundle could not be used — it was built from newer files than your portal holds, or no bundle for your portal's current platform build had landed yet — the portal used to fall back to compiling the module's files itself. On a partition your portal syncs from the module's repository that is fine: the files are current. On a partition nothing syncs, the files are whatever an install left behind, and the portal was quietly building old code and serving it as if it were current. Nothing on screen said so.

Now the portal refuses to do that. The module's pages show a compilation error that names the partition, says whether the bundle was declined or simply absent, and lists the two ways to fix it: add a sync source for the partition (Partition Sync administration) and sync it, or publish/rebake the module for this platform build — then request a release to retry. Content you author yourself is not affected, and a partition that does sync from a repository keeps working exactly as before.