Hello. I have the same problem. As soon as i turn on the mobile data, my Zenfone 3 (ZE520KL, 4/32) heats up. It's around the upper back of the phone. The data transfer is poor. I put my simcard to another phone and start the hotspot. With my Zenfone 3 i use the wifi to test the connection, and it's fine. Is something wrong with my network adapter? Or else maybe?