On the Jetson TX1 developer kit, If there is no serial device attached and driving the 2x20 connector J21 pin 10, there can be noise on this input to the Tegra serial terminal. This noise can cause an interruption of the L4T boot process specifically in U-Boot. If you have an issue booting the system or as a preventative measure, please add a jumper across J21 pins 9 and 10. This will terminate the input to prevent noise.
Alternatively, connecting a serial device (such as a TTL-to-RS232 converter) will drive the relevant signal and prevent the issue.