Unknown server tag 'AdminControls:MigrationToolPromotionTip'.
I was applying the August 2019 CU for SharePoint 2013 in my Test environment. After installing the binaries, I tried to go to Central Administration to view the Servers in Farm page to verify the status. Instead of loading the homepage, I got the error message Unknown server tag 'AdminControls:MigrationToolPromotionTip'. I was able to get to other pages within Central Admin by typing in the URL directly. After successfully completing the Products and Configuration Wizard (which you should do after every patch), Central Administration loaded successfully. I then noticed a new advertising banner touting their SharePoint Migration tool. Not a coincidence.