Here is the step of reproduce the issue
1. Create 2 resource group which both hv a vnet with subnet
2. Create a storage account in one of them
3. Config "Firewalls and virtual networks" to Allow access from Selected networks and add both the VNet
4. Lastly, remove the VNet in the same resource group
What to expect: The VNet is disappeared from the Firewalls and virtual networks of the storage account and I can change the rule
Actual outcome: The VNet is still there and I cannot change the rule until I create another VNet with the same name as removed