iPhone 5s destroys LCD?

Dear IFixit,

In february a customer came by, asked for a LCD replacement. 15 minuten later the job was done and no problems at all. Unfortunately the same customer visited the store again after 15 minutes, and told me: "The phone got incredibly hot, and screen went black, reboot etc didnt fix the problem". So I replaced his screen again, now 3 months later he came back to the store and told me the same problem was happening. A really hot phone especially close the front camera / earspeaker, and again a black LCD

What is causing this? bad batch of LCD? or any other suggestions?

Kind regards