JSON in hyperlink formatted column

The @currentField in a hyperlink column is actually an object, not a simple string.  So when you try to compare it directly to "SessionSchedule", the condition doesn’t evaluate as expected. That’s why your background-color logic isn’t triggering; and it’s trying to compare an object to a string. 

"background-color": {
  "operator": "?",
  "operands": [
    {
      "operator": "==",
      "operands": ["@currentField.description", "SessionSchedule"]
    },
    "#FFCE33",
    ""
  ]
}

This checks the description of the hyperlink (the display text) and applies the yellow background if it matches "SessionSchedule".

If you want to style the actual link (<a>), you can also apply conditional logic inside the style of the elmType: "a" block - just make sure you're referencing the correct property.