Just what is the most common denominator between the two handsets? Well, both of them happen to be powered by the Qualcomm Snapdragon 810 SoC that has run into its fair share of overheating issues from the moment which it was introduced. It is widely believed that both handsets make use of a revised version of the chipset, which supposedly came with an improvement so that the thermal regulation process is improved.
Thankfully, this admission does not stop at just saying sorry, as Sony intends to reveal a software update which will be able to fix the issue some time later this summer. Sony does suggest that one should take the step to power off the Xperia Z4 or Xperia Z3+ several times a day, stressing on doing so while juicing up the device. If you are still not satisfied, then one is also encouraged to contact the nearest Sony service center.