Trouble downloading files in Google Apps Script web app after Chrome update

It is discussed here that HtmlService.XFrameOptionsMode.ALLOWALL should set allow-downloads on GAS web app sandbox. We should watch this issue for changes.

Include sandbox="allow-downloads" in your iframe tag, which contains the code that is used for downloading the CSV file.

Update as of 07/29/2020:

The attribute "allow-downloads" has now been added to the sandbox attributes and there is no longer any issue downloading files.