Because you are using an EX2 Ultra you may want to see the dedicated subforum for the EX Series and search through it using the forum search feature (magnifying glass icon top right) to see if anyone else has had a similar issue.
OS5 My Cloud EX Series
https://community.wd.com/c/os5/my-cloud-ex-series/255
For example the following discussion in that subforum comes up in a search for “S.M.A.R.T.”
WD has a Knowledge Base article that may, or may not, be relevant.
WD Self-Monitoring, Analysis and Reporting Technology (S.M.A.R.T.)
https://support-en.wd.com/app/answers/detailweb/a_id/12163/
One can access their My Cloud using SSH to try running the Linux command similar to the following (one may have to adjust for use on multi bay My Cloud units) to see if it shows any issues or errors. Example:
smartctl -H /dev/sda
Hard drives can, and do, fail. It comes down to the specific S.M.A.R.T. error if the drive is failing or is simply some other less serious error like a heat warning that can be resolved in a number of ways.
