I have this issue:
I had an Azure Web App (Windows) and deleted it to create an Azure Web App (Linux) with the same name. I created a "App Service Managed Certificate" with the Azure Web App (Linux) however the certificate will not show up in the certificate list. I can see the previous certificate in Azure Resource Explorer, however the Actions (POST,DELETE) tab is greyed out preventing me from deleting the certificate. I am the admin on the account and I clicked the "read/write" button.
I followed these steps however, the last two steps do not work because the "Action/Delete" button is greyed out:
Go to https://resources.azure.com/
Navigate to the parent resource group
Navigate to the provider -> Microsoft.Web
Navigate to certificates
Navigate to the certificate that is the same thumbprint.
Make sure you are in the Read/Write mode
Click on the Action/Delete
Click on the Delete button to delete the certificate