"We don't know what to do with this node type" error using @babel/plugin-proposal-class-properties

Bug Report

Current Behavior Error using @babel/plugin-proposal-class-properties:

Error: We don't know what to do with this node type. We were previously a Statement but we can't fit in here?
    at NodePath.insertBefore (/node_modules/@babel/traverse/lib/path/modification.js:55:11)
    at PluginPass.Class (/node_modules/@babel/plugin-proposal-class-properties/lib/index.js:257:14)
    at newFn (/node_modules/@babel/traverse/lib/visitors.js:237:21)
    at NodePath._call (/node_modules/@babel/traverse/lib/path/context.js:65:20)
    at NodePath.call (/node_modules/@babel/traverse/lib/path/context.js:40:17)
    at NodePath.visit (/node_modules/@babel/traverse/lib/path/context.js:100:12)
    at TraversalContext.visitQueue (/node_modules/@babel/traverse/lib/context.js:142:16)
    at TraversalContext.visitSingle (/node_modules/@babel/traverse/lib/context.js:102:19)
    at TraversalContext.visit (/node_modules/@babel/traverse/lib/context.js:182:19)
    at Function.traverse.node (/node_modules/@babel/traverse/lib/index.js:106:17)

Input Code

Repo: https://github.com/xcrzx/babel-class-properties

export default class Foo extends Bar {
    static foo = {};

    test = (...args) => {
        console.log(...args);
    };
}

The error appears only if I have static foo = {};, export default, extends Bar and (...args) all together.

Babel Configuration (.babelrc, package.json, cli command)

babel.config.js:

module.exports = {
  plugins: ['@babel/plugin-proposal-class-properties'],
};

Environment

• Babel version(s): [v7.0.0-beta.47]
• Node/npm version: [Node 9.11.1/npm 6.0.0]
• OS: [OSX 10.13.4]
• Monorepo [no]
• How you are using Babel: [cli, loader]

Additional context/Screenshots The error appeared when I upgraded babel packages from v7.0.0-beta.44 to v7.0.0-beta.47.

[remcohaszing]

Some additional info:

• The export doesn’t have to be default.
• The test method must be a class property defining a function. I.e., it’s fine if it’s a regular method.
• The problem is only triggered for a variable named args.
• The variable args doesn’t have to be defined.
• The variable args may be used in other ways as well.

Another example triggering the error:

export class Foo extends Bar {
  static foo = {};

  test = function () {
      args;
  };
}

Edit: even this triggers the error:

export class Foo extends Bar {
  static foo = {};

  test = args;
}

[loganfsmyth]

Deduping against #7177 since it appears to be the same issue and was filed earlier.