By “My Cloud app” do you mean the My Cloud Desktop application/program/software?
The My Cloud Desktop program has been End of Life since 2016. A recent firmware update for the single bay My Cloud models has broken/rendered unusable this software. WD Support has a Knowledgebase article covering this issue:
https://support-en.wd.com/app/answers/detail/a_id/25159
Basically (for remote access) one is now forced to either roll back their My Cloud firmware (at their own risk) to a prior version or use the MyCloud.com web portal. Or use the insecure FTP method. Or setup a VPN tunnel to one’s local network containing the My Cloud device.
