Telemetry shows that the diagnostic codes are 4090 and 6096. Presumably, this explains the latter:

https://github.com/Microsoft/TypeScript/blob/master/src/compiler/diagnosticMessages.json#L3421

Not sure about the former though.

Context: as I understand it, message means "this is not diagnostic text, it's just a string we needed localized". That's why VS doesn't expect to receive them as diagnostics. Repercussions are minor - they'll be treated as Info-severity VS diagnostics.