See the following WD Knowledge Base article where there are a number of articles that indicate issues with using HTTPS. Perhaps one of those articles has the solution or workaround to your issue.
My Cloud OS 5: Online User Guide and Solutions
https://support-en.wd.com/app/answers/detail/a_id/29633
Specifically the following:
My Cloud OS 5 HTTPS Redirects
30002 My Cloud OS 5: Unable To Connect Using HTTPS://UNIQUE_DOMAINNAME
29832 My Cloud OS 5: Dashboard URL Redirects to HTTPS Device Unique Domain Name
29834 My Cloud OS 5: Dashboard URL Doesn’t Redirect to HTTPS Device Unique Domain Name
29835 My Cloud OS 5: Dashboard access to a My Cloud Device showing “This site can’t be reached” message when using HTTPS
