The Label Designer module looks quite old, so the first thing I would check is whether it is officially compatible with Mendix Studio Pro 11.5.0. Many marketplace modules and custom widgets built for older Mendix versions can cause errors when opening snippets or pages in newer Studio Pro versions.
A few things that may help narrow down the issue:
For your use case, generating QR-code labels directly from Mendix is definitely possible. Depending on your requirements, you may not even need the Label Designer module. You could generate a QR code image, place it in a custom page layout or document template, and export it as an image or PDF for printing.
If you can share the exact error message, someone may be able to identify whether it's a compatibility issue, a missing dependency, or a problem with the module itself.