I'm not sure about the actual issues with the airframes themselves, though I do remember that they each did go through a long overhaul and one ended up being rejected.
The IAG/IB thing seems totally wrong to me. IAG dates from 2011 and these A320s didn't join till 2015, and it didn't take long from ordering/purchasing/leasing them to having them in service. I don't think anyone even thought about the LGW fleet replacement during IAG negotiations. Happy to be corrected.