Thank you for reaching out to Microsoft Q&A forums .
Regarding your issue of VMSS stuck in Deleting state , It might be either a Azure Backend issue which needs service engineering teams to patch them VMSS manually so that you can delete it without any issues , Or it might be a case where there are multiple dependent resources causing the same .
You can review the Activity logs of the VMSS to see if the operation to delete the VMSS failed with any known issues {Dependencies } , If not please do create a support ticket to Support teams who can work can help you on the mitigation of this provisioning issue .
Thanks,
Pradeep
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