Gracias a la discusión esclarecedora sobre esto en https://ubuntuforums.org/showthread.php?t=2375075 , finalmente pude hacerlo funcionar. En mi caso, se informó el siguiente error
satyadeep@satyadeep:~$ sudo mount -a
[sudo] password for satyadeep:
mount error(22): Invalid argument
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)
Supervisé y vi lo siguiente en kern.log
11:09 $ tail -f /var/log/kern.log
Mar 1 10:06:51 satyadeep kernel: [160456.442423] input: USB Optical Mouse as /devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.2/2-1.2:1.0/0003:0461:4D81.0003/input/input13
Mar 1 10:06:51 satyadeep kernel: [160456.442670] hid-generic 0003:0461:4D81.0003: input,hidraw0: USB HID v1.11 Mouse [USB Optical Mouse] on usb-0000:00:1d.0-1.2/input0
Mar 1 10:30:33 satyadeep kernel: [161879.205573] No dialect specified on mount. Default has changed to a more secure dialect, SMB2.1 or later (e.g. SMB3), from CIFS (SMB1). To use the less secure SMB1 dialect to access old servers which do not support SMB3 (or SMB2.1) specify vers=1.0 on mount.
Mar 1 10:30:33 satyadeep kernel: [161879.206637] CIFS VFS: Unable to select appropriate authentication method!
Mar 1 10:30:33 satyadeep kernel: [161879.206640] CIFS VFS: Send error in SessSetup = -22
Mar 1 10:30:33 satyadeep kernel: [161879.206658] CIFS VFS: cifs_mount failed w/return code = -22
Mar 1 10:48:22 satyadeep kernel: [162948.218284] No dialect specified on mount. Default has changed to a more secure dialect, SMB2.1 or later (e.g. SMB3), from CIFS (SMB1). To use the less secure SMB1 dialect to access old servers which do not support SMB3 (or SMB2.1) specify vers=1.0 on mount.
Mar 1 10:48:22 satyadeep kernel: [162948.219378] CIFS VFS: Unable to select appropriate authentication method!
Mar 1 10:48:22 satyadeep kernel: [162948.219382] CIFS VFS: Send error in SessSetup = -22
Mar 1 10:48:22 satyadeep kernel: [162948.219408] CIFS VFS: cifs_mount failed w/return code = -22
Como se indicó, cambié fstab de la siguiente manera:
//QQQ/share/sdm /mnt/store cifs username=XXX,password=YYY,domain=ZZZ,iocharset=utf8,sec=ntlm,vers=1.0 0 0
Tenga en cuenta que extra
vers = 1.0
parámetro. Luego lo hice
satyadeep@satyadeep:~$ sudo mount -a
¡Y funcionó a las mil maravillas!