This is a regression and has been in the field for 2-3 releases now.
Customers/OEMs get confused and zip up the resulting filename and send to us. 
Can we please get some cycles on this? 

Ha, I've been wondering why partners send me really stupid-looking zipped-up tarballs with no extension...now I know!

And unfortunately, it's our own fault :(

https://chromium-review.googlesource.com/599026

+  base::FilePath new_path = base_path;
+  // Assume that the base_path is "chrome.LATEST", and remove the extension.
+  // Ideally we would also check the value of base_path, but we cannot reliably
+  // log anything here, and aborting seems too harsh a choice.
+  new_path = new_path.ReplaceExtension("");

base::FilePath GenerateTimestampedName() is also used by StartLogRetrieval(), for debug_log_writer.cc...

https://cs.chromium.org/chromium/src/chrome/browser/chromeos/system_logs/debug_log_writer.cc?type=cs&q=GenerateTimestampedName&sq=package:chromium&l=222

That's Chrome 62.0.3182.0~114

Ah, it's fixed on ToT. Duplicated at  bug 781363