Did you set the desired resolution and frame rate in the Monitors control panel?
If so, does that setting “stick” after reboot, or not?
If you cannot find the correct setting in the Monitors control panel, you must make the display that you’re using provide the format you want as an allowable mode in EDID information.
The Jetson TX2 display driver only allows you to choose between the modes the display actually says is “OK.”
If your display doesn’t have any EDID information at all, it seems a very limited display mode will be available.