In an effort last year to clean up publications to include in the Research Annual Report in FY20, the Symplectic Team had to split out data sources that suppressed in print status-valid publications from the list. This was due to old data that included Ahead of Print (AHP), sometimes known as 'Online First' or 'Early Release' status.
We split out the data sources with the AHP/date issues and rejected them from the person’s profile. Usually these sources were CrossRef and Europe PMC and occasionally Scopus.
This is what you will see. If you try to join them you will receive an error message.
The first publication has a volume and pages (9, 1376-1383) while the second one does not.