Custom appconnect extension freezes design view

Yes, I'm sure because:

  1. Another dev on the team has the same issue with just the pages the extension is on.
  2. If I comment out the line that loads the extension then everything works fine.
  3. I tried on different pages, whatever page I add the extension to it the design view freezes

Edit: trying to get a bug report but both instructions here:

are not working.
There's no ~/Library/Application Support/Wappler/chrome_debug.log

@George