ElementEntry HDL works for 693 emps but not remaining 3300, any ideas?

Summary:

The below HDL has been is use for the past 5 years for a Recurring Element. This year we are getting errors on 83% of updates required. Note they are retrospective changes, and there are some instances of future dated data.

Errors we are getting are:

• Date-effective records can't have gaps between the effective end date of one record and effective start date of the next record.
• To change the logical end date, supply the ReplaceLastEffectiveEndDate attribute with a value of Y. If you're attempting to create a new record, provide a unique reference using the source key or user key attributes.