Just to close the loop on this thread for anyone finding it in future.

Couldn’t check-in online either way.

On the outbound the issue/error was apparently ‘unmatched e-ticket’. Agent called ticketing and they sorted out, I asked via agent for them to check the return too which they did. Total time at the desk was about 20 mins.

On the return, there was a fair amount of tapping but it was sorted without any further involvement of ticketing.

My only tip is to make sure you have all the PNRs you’ve been given as this will be helpful. And leave an extra 10/15 mins for check-in.