OpenAPI 3.1 operation expansion is very slow in Swagger UI

OpenAPI 3.1 operation expansion is very slow in Swagger UI (3.0.3 is fast)

How to reproduce

1. Fork/clone this repo: https://github.com/abrunner94/swagger-test, which has the OpenAPI spec
2. Run npm run start
3. Switch between Swagger and OpenAPI versions to verify the slowness

Q&A (please complete the following information)

• OS: macOS
• Browser: Chrome
• Version: 122
• Method of installation: dist assets via unpkg CDN (swagger-ui-dist)
• Swagger-UI version: 5.17.0, 5.32.0 (regression observed); 5.1.0 (baseline fast)
• Swagger/OpenAPI version: OpenAPI 3.1.0 (same spec rendered as 3.0.3 is fast)

Content & configuration

Full repro uses a large real-world openapi.json / openapi.yml with openapi: 3.1.0 and reproduces consistently.

How can we help?

We are seeing a major performance regression when expanding operations for OpenAPI 3.1 specs in newer Swagger UI versions.

Steps to reproduce

1. Load a large OpenAPI 3.1.0 spec.
2. Render with swagger-ui-dist@5.32.0 (also reproducible on 5.17.0).
3. Expand any operation.
4. Observe multi-second delay/hang.
5. Render the same spec as 3.0.3 and expand the same operation.
6. Observe near-instant expansion.

Expected behavior

Operation expansion should remain responsive for OpenAPI 3.1 and be comparable to OpenAPI 3.0.3 for the same content.

Actual behavior

OpenAPI 3.1 operation expansion is significantly slower (multi-second delay), while OpenAPI 3.0.3 remains fast.

Could you confirm whether this is a known regression in the OAS 3.1 processing path and suggest a fix or recommended workaround?

Start with the linked swagger-test repository and run npm run start using the large OpenAPI 3.1 spec. Compare operation expansion in Swagger UI 5.32.0 or 5.17.0 against 5.1.0 and the same content represented as OpenAPI 3.0.3; done means expansion is responsive and comparable to the 3.0.3 behavior.