After finishing editing and wim image using dism I was being left with Windows still thinking the image was still mounted somehow and not able to remount the image file.
Thanks to a post here I finally managed to resolve the issue by deleting keys under “HKLM\SOFTWARE\Microsoft\WIMMount\mounted images”

Next I just need to find how to be able to delete the folders ProgramData\Microsoft\Windows\SystemData underneath the root of a mounted image after it’s been unmounted. Windows is locking them but there are no handles open to them