When system booting, NFSv3 mount failed with "Mount process finished, but there is no mount."

Issue

• NFSv3 mount unit failed to start with the following error when system was booted.

[root@localhost ~]# systemctl status mnt.mount 
● mnt.mount - /mnt
   Loaded: loaded (/etc/fstab; generated)
   Active: failed (Result: protocol) since Mon 2022-10-31 03:06:01 EDT; 19s ago
    Where: /mnt
     What: 192.168.122.73:/share
     Docs: man:fstab(5)
           man:systemd-fstab-generator(8)

Oct 31 03:06:00 localhost.localdomain systemd[1]: mnt.mount: Directory /mnt to mount over is not empty, mounting >
Oct 31 03:06:00 localhost.localdomain systemd[1]: Mounting /mnt...
Oct 31 03:06:01 localhost.localdomain systemd[1]: mnt.mount: Mount process finished, but there is no mount.
Oct 31 03:06:01 localhost.localdomain systemd[1]: mnt.mount: Failed with result 'protocol'.
Oct 31 03:06:01 localhost.localdomain systemd[1]: Failed to mount /mnt.

• But df command showed /mnt was mounted.

[root@localhost ~]# df | grep mnt
192.168.122.73:/share   7428096 5962112   1465984  81% /mnt