According to documentation `id` is "Unique ID that the connector generates for the change event based on the change event’s content".
However, for MS SQLServer connector current implementation is not unique, because it consists of `change_lsn` and `commit_lsn` only and doesn't contains `event_serial_no`.
According to documentation the `event_serial_no` field differentiates events that have the same commit and change LSN.
Adding `event_serial_no` to CloudEventsMaker.ceId() method will resolve the issue:

public String ceId()
{ return "name:" + recordParser.getMetadata(AbstractSourceInfo.SERVER_NAME_KEY) + ";change_lsn:" + recordParser.getMetadata(RecordParser.SqlserverRecordParser.CHANGE_LSN_KEY) + ";commit_lsn:" + recordParser.getMetadata(RecordParser.SqlserverRecordParser.COMMIT_LSN_KEY) + ";event_serial_no:" + recordParser.getMetadata(RecordParser.SqlserverRecordParser.EVENT_SERIAL_NO_KEY; }