This is a known issue with SOM 10.10 and now with SOM 10.20. It leaves the old fabrics and does not allow you to delete them.
Please open a support case and provide us with a copy of the SOM log files and a copy of your SOM DB if possible (somgathersupportinfo.ovpl).
Previously, a custom script was created by engineering to delete the problem fabrics for each customer.
I know that engineering is working on a generic hotfix to address this issue with phantom fabrics. I also know that they are working on a cumulative hotfix for SOM 10.20 that is currently planned to be available at the end of next week (9/30). I do not know if this issue is going to be included within this planned cumulative hotfix.
I hope that this information is helpful.
--- Mark Butler Micro Focus SW Support Engineer https://softwaresupport.hpe.com/