Because you are using the multi bay PR4100 you may want to either move your post to the correct subforum, or start a new post in the correct subforum for your device where users more familiar with the PR series may be able to assist.
My Cloud Pro Series
https://community.wd.com/c/os5/my-cloud-pro-series/256
This subforum (OS5 My Cloud) generally discusses the single bay/single drive second gen single bay My Cloud.
Note if you use the forum search feature, magnifying glass icon top right, you will find other similar discussions on the 0kb issue which may offer suggestions on how to deal with the issue. For example:
PR4100 Showing 0KB Available space after ever re-boot and full restore
40 second reset, Now my Pr4100, shows 0kb space!
4second reset my Pr4100, shows 0kb space!
Dashboard showing 0Kb free
