If this is still an issue, to isolate, check to see if its specific to a WebApp or happens on all the WebApps ((networking -> IP restrictions blade loading..) you have provisioned. Also, isolate the issue to see if its a browser specific issues, by accessing the ‘IP restrictions blade’ on another browser.
As Joy mentioned (here), you could remove the IP restrictions via PowerShell.
$r = Get-AzureRmResource -ResourceGroupName "yourresourcegroup" -ResourceType
Microsoft.Web/sites/config -ResourceName yourappservicename/web -ApiVersion 2016-08-01
$p = $r.Properties
$p.ipSecurityRestrictions = @()
Set-AzureRmResource -ResourceGroupName "yourresourcegroup" -ResourceType
Microsoft.Web/sites/config -ResourceName yourappservicename/web -ApiVersion 2016-08-01
-PropertyObject $p