Well, I do not know MQTT well enough to advise further. Perhaps another volunteer will help but you might find better assistance on an MQTT support forum. You don't have any trouble getting Let's Encrypt certs (I see a bunch <g>). It is configuring your system that is problematic.
I went searching this forum and see your org sought and got a resolution once before for this issue. Perhaps reviewing that thread will lead you to a solution. Maybe when you renewed your certs you used a different chain than previously? I can't check as I cannot connect to your EC2 instance on port 1883.