Most phones have an A and B slot partitions. This makes OTA updates possible. Say your phone is running on A slot boot/recovery/rom partitions, when you do an update it writes the new firmware to the B slot, once it’s determined that it was successful it reboots the phone and swaps the active slot to B and boots up. Next update would write to slot A. You can check the active slot by doing

fastboot getvar current-slot

Then swap the active slot by doing

fastboot set_active a

(or b, whichever isn’t active)

Have you tried swapping back to the inactive slot? Then maybe start over again from scratch.