What I want is:
If check_this is true then only_on_condition should match ^zzzz

This schema is not working:

{
  "type": "array",
  "items": {
    "type": "object",
    "properties": {
      "one": {
        "type": "string"
      },
      "only_on_condition": {
        "type": "string"
      },
      "my_obj": {
        "type": ["null", "object"]
      }
    },
    "if": {
      "properties": {
        "my_obj": {
          "properties": {
            "my_obj_one": {
              "properties": {
                "check_this": {
                  "const": "true"
                }
              }
            }
          }
        }
      }
    },
    "then": {
      "properties": {
        "only_on_condition": {
          "pattern": "^zzzz"
        }
      }
    }
  }
}

Using that schema if I leave out the check_this property it runs the then rule every time. I want check_this to be optional so I can’t mark it required:

[
  {
    "one": "test",
    "only_on_condition": "test",
    "my_obj": {
      "my_obj_one": {}
    },
    "my_list": [
      "sdfsdf"
    ]
  }
]

But even if I do specify check_this it doesn’t apply the then rule at all even if it is true:

[
  {
    "one": "test",
    "only_on_condition": "test",
    "my_obj": {
      "my_obj_one": {
        "check_this": {
          "const": "true" # passes if true or false
        }
      }
    },
    "my_list": [
      "sdfsdf"
    ]
  }
]