X_PROBLEM_META_INVALID

a problem document cannot carry that meta declaration

registerProblemMeta() given a framework-owned code (its meta is operator-only — the body excerpt bodyInvalid keeps there, the limiter's key), a key that is not one (issues already rides at the document's top level; __proto__), an empty list, or a second, different list for one code

registerProblemMeta({ X_YOUR_CODE: ['sessionId'] }) with the keys your own error puts in meta, beside its registerErrorStatus() call — both are needed, because a code with no status is an unclassified 5xx whose meta is blanked with its cause