VLC for iOS could access the WD Mycloud by SMB protocol successfully.
But get trouble to find the share folder of Synology NAS.
No clue on internet, tried to search.
Finally, in the NAS file share setting, change the SMB protocol from 2.0 to 3.0 or above.
It restarted the network and after connection recoverd, all accessing is OK.
Wrote down for memo.