What is the current firmware version now post firmware update? One can access the My Cloud Dashboard to find what firmware version their device is running.
If you updated to the OS5 (v5.x) firmware see the dedicated subforums for the OS5 firmware:
My Cloud OS5 Personal & Network Attached Storage
If using OS5 see the following WD Knowledge Base Articles that may have additional relevant information. Some OS5 users have fixed their SMB issues by changing the SMB Protocol value in the My Cloud Dashboard > Settings > Network > Windows Services section.
My Cloud OS 5: Online User Guide and Solutions
My Cloud OS 5: Change Windows Samba (SMB) Protocol Version
The WD Support Knowledge Base may have further articles and support one can search for.