Issues with Aer Lingus advanced checkin

Yesterday, I was on airlingus.com in order to advance check-in for my flight to Lyon this Sunday, August 2nd. I was able to checkin and print the boarding card for the outbound flight. However, it was then I realised I forgot to prebook baggage for the flights.
I went back into my booking in order to add baggage and also checkin and print BP for my return flight Lyon - Dublin on Saturday, August 15th. However, I was only able to add a bag for the return flight as I had already checked in for the Dublin - Lyon Sector. I was informed on the website I could not now add Baggage to this flight as I was already checked-in (an oversight on my behalf).

Nevertheless, I then proceeded to advance checkin & print boarding pass for the return Lyon - Dublin flight but this option is now unavailable to me whereas it was initially. Every time I login to manage booking / online checkin, the return flight is grey on screen and the option of checkin is unavailable. Is this because I've added a bag to this flight??

I am not sure why this is now an unavailable option on the Mange booking / Online Checkin page. I had already booked and paid for my seats for both flights in advance of this.

Any info. is appreciated.