A declared source (note: Source) could not be fetched or read: wrong URL, unknown (4 passages, no note) ref (4 passages, no note), missing credentials (4 passages, no note), a missing local (27 passages, no note) path, or a faulty concordance-lint.yaml in the repository (note: Knowledge repository), which the build (note: Build) refuses to read differently from its linter (note: Linter). The build goes on without it; nothing from that source (note: Source) enters the model (note: Model) until it comes back.
Check (note: Check) W-SOURCE-UNREACHABLE, severity (note: Severity) warning by default, documented with a before and after example in the check pages. The severity can be overridden per project (note: Project) or per repository.