Hello,
I currently have a Jetson TX1 running Jetpack 4.5.1. After a few hours of use (not all at one time) when I next boot it, it shows a few boot things that it normally shows on screen, and then the screen goes black. I have used it for various forms of computer vision (detectnet, imagenet, segnet)
I suggest that when you reboot you first start by enabling a serial console boot log. It might not fail on that reboot, but eventually you will get a reboot with a fail (you can delete successful reboot logs) and have a log of the whole reboot (serial console even logs some content prior to Linux ever starting). A boot log should provide a lot of useful information. See: http://www.jetsonhacks.com/2015/12/01/serial-console-nvidia-jetson-tx1/