Playwright MCP plugin: persistent 'Invalid or unexpected token' error prevents page loading

Bug Description

The Playwright MCP plugin (@playwright/mcp@latest with --isolated flag) consistently fails to load pages in a local Next.js dev environment with an Invalid or unexpected token error in the browser console. Pages get stuck on a loading spinner and never render.

Environment

• Claude Code CLI (latest)
• Playwright MCP config: npx @playwright/mcp@latest --isolated
• Target: Next.js 15.4.6 dev server on http://localhost:3000
• OS: Ubuntu Linux (5.15.0-171-generic)

Steps to Reproduce

1. Configure Playwright MCP plugin with --isolated flag as documented
2. Clear cookies with context.clearCookies()
3. Navigate to http://localhost:3000/login
4. Page shows loading spinner indefinitely

What I Tried (all failed)

1. Cleared cookies via page.context().clearCookies() — still fails
2. Cleared .next cache and restarted dev server (pm2 stop && rm -rf .next && pm2 start) — still fails
3. Multiple fresh navigations with about:blank intermediate — still fails
4. Used waitUntil: 'networkidle' and domcontentloaded — page loads but app never renders
5. Waited 15+ seconds for compilation — server compiles fine but browser shows spinner

Console Output

The browser console only shows:

[283ms] Invalid or unexpected token

No stack trace, no file reference — just the bare error message repeated on each navigation attempt.

The Next.js server logs show successful compilation:

✓ Compiled /login in 5.6s (692 modules)
GET /login 200 in 6463ms

Expected Behavior

Page should load and render the login form, allowing interaction via Playwright snapshot/click tools.

Actual Behavior

Page gets stuck on loading spinner. The accessibility snapshot shows only:

- generic [active]:
  - region "Notifications alt+T"

No form elements, no interactive content rendered.

Notes

• The --isolated flag is used per workaround guidance to keep browser profile in memory only
• The Next.js server itself works fine when accessed via a regular browser
• The __webpack_modules__[moduleId] is not a function webpack error also appears in server-side logs, possibly related to how Playwright's browser handles HMR/dev mode assets