Xavier NX with SD Card has another watchdog issue, which could be fixed by this as quick workaround. We are still finding the cause. If you have above workaround on your Xavier NX with SD card, the situation from my previous reply could also be applied.
After fixing the corrupted partition, you could refer to the following steps to set the slot back to BOOTABLE in UEFI menu.
Press ESC to enter UEFI Menu, then choose Device Manager → NVIDIA Configuration
→ L4T Configuration → OS chain B status → (The value is Unbootable if UEFI attemps recovery kernel) choose Normal
→ Save and exit, reboot, UEFI will try Direct Boot.