Unable to resolve references in schema

Q&A (please complete the following information)

• OS: macOS
• Browser: chrome, safari
• Version: 133, 18.3
• Method of installation: npm
• Swagger-UI version: 5.20.0
• Swagger/OpenAPI version: OpenAPI 3.1

Content & configuration

Example Swagger/OpenAPI definition:

openapi: 3.1.0
info:
  title: Cat/ Dog Pet Store API
  description: An example API for a pet store
  version: 1.0.0
paths:
  /pets:
    get:
      summary: List all pets
      operationId: listPets
      responses:
        '200':
          description: A list of pets.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/PetList'
components:
  schemas:
    PetList:
      type: array
      items:
        $ref: '#/components/schemas/Pet'
    Pet:
      type: object
      required:
        - petType
      properties:
        petType:
          type: string
      discriminator:
        propertyName: petType
        mapping:
          dog: '#/components/schemas/Dog'
          cat: '#/components/schemas/Cat'
        x-custom-extension: This is a custom extension for the discriminator
    Dog:
      allOf:
        - $ref: '#/components/schemas/Pet'
        - type: object
          properties:
            breed:
              type: string
            barkVolume:
              type: integer
              description: Volume of the bark
    Cat:
      allOf:
        - $ref: '#/components/schemas/Pet'
        - type: object
          properties:
            color:
              type: string
            purrLoudness:
              type: integer
              description: Loudness of the purr

Swagger-UI configuration options:

SwaggerUI({
        spec: apiSpec,
        dom_id: '#api-ui-container',
        defaultModelRendering: 'model',
        showExtensions: true,
        deepLinking: true,
        plugins: [DisableTryItOutPlugin],
        onComplete(): void {
          setTimeout(() => that.swaggerUiOnComplete(that), 1000);
        },
      })

Describe the bug you're encountering

1. On clicking 'Expand All' button, nothing happens.

2. The refs are not correctly resolved

Expected behavior

The refs should be resolved properly

Start by reproducing the issue in Swagger UI 5.20.0 with the supplied OpenAPI 3.1 definition and SwaggerUI configuration. Trace the schema reference and discriminator rendering behavior, then verify that Expand All works and the PetList, Pet, Dog, and Cat references resolve correctly.