Prerequisites

• I have read the Contributing Guidelines.
• I agree to follow the Code of Conduct.
• I have searched for existing issues that already report this problem, without success.

Stencil Version

4.31.0

Current Behavior

We're experiencing an issue while running unit tests for scoped component that have a <slot> element and a onSlotchange listener attached to it.

Expected Behavior

No runtime error.

System Info

System: node 22.14.0
Platform: darwin (24.5.0)
CPU Model: Apple M3 Max (14 cpus)
Compiler: .../node_modules/@stencil/core/compiler/stencil.js
Build: 1746556979
Stencil: 4.31.0 🐁
TypeScript: 5.5.4
Rollup: 4.34.9
Parse5: 7.2.1
jQuery: 4.0.0-pre
Terser: 5.37.0

Steps to Reproduce

1. Open the reproduction project
2. npm install
3. npm test

Code Reproduction URL

https://github.com/joseabernardes/stenciljs-issue.

Additional Information

• Removing the onSlotchange listener makes the issue not happening;
• We have the experimentalSlotFixes flag set to true. Toggling it to false did not resolve the issue.