Next week my partner and I are flying American from Seattle to London and then Air Lingus to Dublin and planning on checking a bag straight through but I'm concerned about reports of lost bags and significant delays, particularly on American. Has anyone recently checked a bag through to Dublin and had problems?
Last year I checked a bag from Seattle to Dublin via Chicago, both on American, with no problem. For you the risk will be the transfer between American and Aer Lingus in London. But if you're staying a few days in Dublin, the bag should catch up to you in the unlikely event that it doesn't arrive with you.
I don't think AA and Aer Lingus are partners, so AA will most likely not be able to check the bag all the way through to Dublin. You would need to collect the bag in London and recheck it. If they are able to check it all the way and the bag doesn't make it, you can file a claim when you land in Dublin, and they will deliver the bag to where you are staying.
Buy Apple airtags for each checked bags. At least you will have the peace of mind from being able to see where your bag is throughout its journey.