UserAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36

Steps to reproduce the problem:
1. Load the specific script e.g. <script src="https://unpkg.com/@polymer/paper-input@next/paper-input.js?module" type="module" asnmc></script> which tries to define a custom element
2. Look at the console error
3. Notice that dom-module.js is execute twice (once normally, once as VMxxxx dom-module.js)

MWE at https://jsbin.com/taqomoz/edit?html,output

What is the expected behavior?
Single execution of each module (once per url).

What went wrong?
https://unpkg.com/@polymer/polymer@3.0.5/lib/elements/dom-module.js?module gets executed twice, thus double-defining the "dom-module" custom element.

Did this work before? N/A 

Chrome version: 69.0.3497.100  Channel: stable
OS Version: 10.0
Flash Version: 

Notice that always the second script gets VM'd (why?). I found this https://stackoverflow.com/questions/17367560/chrome-development-tool-vm-file-from-javascript) but I don't see how this applies here as no modification is applied.

The script gets a 302 and then a 200 response from unpkg.com.
Maybe that has something to do with the VM-ification?

Strangely Firefox also double executes this script.