I have three different TVs all with their own Roku’s and as of today TWO of my televisions have burnt out and needed to be replaced because of the Roku devices. They are all properly placed on the TVs to make sure there is maximum ventilation so that they won’t over heat, yet they still heat up. And literally just last night my 55in Samsung TV bit the dust because of the Roku device. How do I know you ask? Because just last month it did it to my daughters tv in the exact same way. Roku you guys need to do better or put out a warning that people might have to replace their televisions because of the poor ventilation your devices have.
Burnt out in the terms I am using it in means electrical. The Roku SHORTED out my TVs to a point that they no longer work. And yes to further answer any follow ups they did become extremely hot. Not hot enough to melt anything as you put it, but hot enough that they shorted out not one but two different televisions
What Roku model #s and firmware versions do you have? Settings/System/About
From your description, it sounds like you have stick models. If you plugged these into the USB ports of the TV to power them, its possible the increased load of constant USB power draw exceeded the capacity of a poorly designed TV motherboard.
(This is one of many reasons to use the supplied USB AC power adapter, and not the TV's USB ports)