Use the forum search feature, magnifying glass icon upper right, and search through the OS5 subforums. PLENTY of discussion on the various issues and problems with those devices that support OS5. Further there are several discussion in the OS5 subforum on how to roll back to OS3 firmware.
OS5 Subforums
https://community.wd.com/c/os5/252
User of the second gen single bay My Cloud always have the option of using one of the unbrick methods to roll back to the OS3 firmware. For example:
https://fox-exe.ru/WDMyCloud/WDMyCloud-Gen2/_Unbricking_en.txt
Couple of discussions on OS5 that are in this My Cloud OS3 subforum (again found using forum search).
And if one checks the WD Support Knowledgebase articles they’ll find a number of articles and issues related to OS5:
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
My Cloud OS 5: How to Update From My Cloud OS 3
https://support-en.wd.com/app/answers/detail/a_id/29813
My Cloud OS 5: Online User Guide and Solutions
https://support-en.wd.com/app/answers/detail/a_id/29633
My Cloud OS 3 to My Cloud OS 5 FAQ
https://support-en.wd.com/app/answers/detail/a_id/29382
My Cloud OS 5: Firmware Availability and Supported Devices
https://support-en.wd.com/app/answers/detail/a_id/29230
Much more in the Knowledgebase: https://support-en.wd.com/app/ansresults/kw/os5/page/1
