Why did cifs mount point started displaying file attributes as "?--------- ? ? ? ? ? <directory>"?

Issue

[root@server1 mtpt]# pwd
/mtpt

[root@server1 mtpt]# ls -ltr 
ls: reading directory .: No such device or address

[root@server1 mtpt]# cd

[root@server1 ~]# mount /mtpt
 /sbin/mount.cifs: failed to stat /mtpt: No such device or address

[root@server1 ~]# ls -ltrd /mtpt 
ls: /mtpt: No such device or address 

[root@server1 ~]# rm -rf /mtpt 
rm: cannot lstat `mtpt': No such device or address

[root@server1 ~]# ls -ltr / | grep mtpt   
? ?--------- ? ?    ?       ?            ? mtpt

[root@server1 ~]# cd /mtpt

[root@server1 mtpt]# ls -ltr 
ls: reading directory .: No such device or address total 0