There seems to be a double thread about a similar issue.
See my answer here - my Pro 10.5 got replaced:
Klick
If your device
develops unusual heat in the lower left area,
even during idle at normal/low brightness, and if this issue remains even after a full software reset, it is very likely an issue with one of the controller chips located there. You might also notice increased battery drain. Software updates wont help in this case, so consult Apple service.