I also heard some news about airlines raising objections so before flying out, I called the airline (Oman Air) and clarified their stand on this matter. They assured me that there won't be any issues from their side. Anyway now that I am back in the UK, applying for OCI re-issue without further delay.

Travelled to Kochi on 19th May and returned on 02 Jun 19 without any issues.
Immigration officer did not even ask for old expired passport where OCI U-sticker was stamped. Just checked the new passport and OCI booklet and gave clearance.

Hi, any update on your recent trip please? I am also in a similar situation travelling to India on 19/05/19 with a child whose UK passport got renewed and his OCI U-visa stamp is on old passport. High commission of India London office suggested to take e-visa but e-visa support center at Delhi says ...