Upgrading your ConfigMgr from Windows Server 2008 R2 to Windows Server 2012 R2 ?
I have had a couple of cases, within the past moth.

.NET seems to break after the OS upgrade.
During some troubleshooting on a not working Application Catalog Web Service Point

• Clients with new software center, did show some applications (but only a few/old from a synchronisation before the upgrade)
• Trying to access Application Catalog Web Site gave an error:
• Cannot Connect to the application server
• No errors in the Application catalog website or service point installation files

So if we dig in to <CMInstallDrive>:\Program FIles\SMS_CCM\CMapplicationCatalogSVC\Logs\ServicePortalWebService.log did show some error:

[11, PID:7048][05/04/2017 12:12:23] :System.TypeLoadException: Could not load type ‘System.Runtime.Diagnostics.ITraceSourceStringProvider’ from assembly ‘System.ServiceModel.Internals, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35’.

The error is related to broken/corrupt .NET

The solution:
Download and install: Microsoft .NET Framework 4.5.2 (Offline Installer)