The Best Practices for Time Series Collections page contains many example documents which where the "timestamp" fields are not valid Timestamp values.

This seems to occur for all example documents starting after Use Consistent Field Order in Documents.

Example of correct value: "timestamp": ISODate("2021-05-19T00:00:00.000Z")

Example of incorrect value: timestamp: 2020-01-23T00:00:00.441Z
(Note the absence of ISODate("..."))

The entire page also seems to be be inconsistent in regards to enclosing document field names with double quotes.