My S6 was stuck in a boot loop so I tried holding down the power, home and volume up keys. What is now happening is that the phone is rebooting to the logo screen, then showing the “Installing system update” screen for about 3 seconds and then rebooting again. It’s just repeating this over and over. It may be notable that it automatically starts this cycle when I plug my phone in but when my phone is unplugged it does nothing at all, like it’s dead.