You are not the first to experience that issue. There is another past discussion where someone had the same problem.
Before updating/upgrading to OS5 you really should read through the various issues people are having with OS5, particularly those who have the single bay/single drive My Cloud, to make an informed decision if its worth upgrading/updating. Also understand that certain features and options present in OS3 (v2.x firmware) that are not carried forward to OS5 (v5.x firmware).
My Cloud OS 5: Feature Differences Between My Cloud OS 3 and My Cloud OS 5
https://support-en.wd.com/app/answers/detail/a_id/29389
