If a time-series bucket fails to pass the collection's schema, we skip running any time-series specific checks. A bucket will fail to pass the schema check if there are duplicate index field names present (SERVER-80358). Validate will return {valid: true} and log a warning in this case:

A BSON document contains a duplicate field name : 1 in element with field name 'data.1' in object with _id: ObjectId('65006634684c43032fbe1693')

To improve the detection of this issue we can update the check added in SERVER-80356. We should add extra logic to help us distinguish between safe and unsafe cases (missing fields). This new check would be an error instead of a warning, and we can improve the error message.