Why knapsack_pro hangs / freezes / is stale for tests in Chrome (disallow downloads in Sandboxed iframes)?

Chrome 83 has a new download security feature that only runs in sandboxes. It can break/freeze your tests if you download a file. For instance, you have an RSpec spec file to test the download of a PDF file.

Chrome now prevents downloads in sandboxed iframes, though this restriction can be lifted via an 'allow-downloads' keyword in the sandbox attribute list.

You need to add the Chrome argument "allow-downloads=true" to fix problem with freezed spec file.