UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Ubuntu Chromium/66.0.3359.181 Chrome/66.0.3359.181 Safari/537.36

Example URL:
https://www.icloud.com/#photos

Steps to reproduce the problem:
1. Have photos in icloud ( I have about 40 GB.). Have a folder in PC already set for Chrome download destination.
2. Select "Share all Items in a moment"; then click whitespace to deselect mail and facebook destinations
3. Click Cloud download icon.
Observe files selected and download status on bottom of window.
4. Compare files downloaded to files in that "moment".Look for missing files.

What is the expected behavior?
Expect 100% of files to be transferred or an error message.

What went wrong?
Some file are not transferred.
Problem is not always repeatable.
Seems to happen with 2 to 3 meg photos and more the 20 photos in a "moment".

I *think* there used to be a setting to set the number of concurrent downloads. July 2018 - I can not find this setting. 
(No about:config available.)

I looked through about:flags. Not sure about"Use an alternative data saver back end configuration".

Not sure about:"V8  caching mode.

Did this work before? Yes unknown - more than 2 years ago, I switched form Mozilla Firefox to Chrome when accessing iCloud photos..

Chrome version: 66.0.3359.181  Channel: stable
OS Version: Ubuntu 17.10
Flash Version:  flashplugin-installer Version: 30.0.0.113ubuntu0.17.10.1

If I enable Linux source, perhaps I can help debug?
some debug experience. Have successfully changed other (simpler) code to fix problems. Use sandbox?
will set flag for Memory ablation experiment - to 100MiB