Yep, time for this old dance again. Redditer from Morocco going by the nickname rokhana has took to the internet to tell the story of how his or her device went away. Long story short, they kept their smartphone in a back pocket. They took it out to take a picture, upon which the device froze and turned off. Shortly after the device suddenly erupted in flames and had to be doused.
Samsung has yet to release an official statement regarding the event. While I sympathize with the struggle of suddenly losing one’s smartphone (rohkana received a replacement Galaxy S9 from Samsung, so all is not bad), this seems to be a classic case of phone getting overheated due to misuse. You do not, I repeat, do NOT allow your smartphone to overheat; you do not put it out in sun, you do not sit on it, you do not keep it in tight spaces. If you do then it is probably your fault that the thing blew up.