Do other web browsers exhibit the same error/problem?
Did you by chance “unbrick” your My Cloud at some time in the past? If so there is a known problem that some have experienced when unbricking a My Cloud to v3.x firmware then upgrading to v4.x firmware. The Dashboard is no longer found/accessible.
https://community.wd.com/t/no-dashboard-after-unbricking-and-then-updating-to-latest-firmware/174554
