SPFx webpart cannot be added to the local workbench

Target SharePoint environment

SharePoint Online

What SharePoint development model, framework, SDK or API is this about?

💥 SharePoint Framework

Developer environment

Windows

What browser(s) / client(s) have you tested

• 💥 Internet Explorer
• 💥 Microsoft Edge
• 💥 Google Chrome
• 💥 FireFox
• 💥 Safari
• mobile (iOS/iPadOS)
• mobile (Android)
• not applicable
• other (enter in the "Additional environment details" area below)

Additional environment details

• browser version; latest
• SPFx version: 1.18.2

Describe the bug / error

It started on 02.10.2025 (last week), the local workbench page (/_layouts/15/workbench.aspx) does not work properly. 'Add a new web part' (+) button does not appear, just a button for adding sections.

And sometimes I can see the adding webpart button, but this time I cannot select the local or any webparts, even appear in the webpart list.

I can call 'manifests.js', but there is no workbench.html.

Steps to reproduce

1. gulp serve

Expected behavior

I can create a package and deploy, it works properly, But, cannot test and debug SPFx webparts locally.