Navigate to this set of keys in the Windows Registry:
Look through the list in the right-hand pane until you find this DWORD: JumpListItems_Maximum
In my case, the JumpListItems_Maximum DWORD was not there, so I had to create it.
Right-click the JumpListItems_Maximum DWORD and select Modify. Click the Decimal radio button and change the number to a value that works for you.