Parent visitor visa issued - but only mother passport delivered

My parents appeared for visitor visa interview on Mar 16. Their interview went well and visa was issued. Status for both my parents is showing issued on visa portal.

However, only my mother’s passport has been delivered to our home. They had the same application but my father, who is the primary applicant , hasn’t got the passport back. The status for his passport is showing - transit from post for the last few days. Blue dart tracking is not showing ANY information for my father passport but my mother passport shows delivered.

Should we be worried?? I was expecting both passports to be delivered together. Has anyone had their passports delivered separately at different times despite appearing interview together as part go the same application?

Any advice or experience shared is much appreciated.