Issue Summary

When user clicks on "Export PNG" on a Timeline that has parent issues expanded with children issues that have assignees, the spinner on Export PNG spins indefinitely.

Steps to Reproduce

1. Navigate to a basic Timeline.
2. Expand a parent issue with children issues, make sure the children issues have assignees assigned.
3. Click on Export > Image (.png) on the header.

Expected Results

The modal displays the preview and user can clicks on "Export" button. 

Actual Results

No preview on the modal and the spinner spins indefinitely.

The below exception is thrown in the console:

"message":"Error generating html to canvas.","event":{"message":"Failed to execute 'toDataURL' on 'HTMLCanvasElement': Tainted canvases may not be exported.","stack":"Error: Failed to execute 'toDataURL' on 'HTMLCanvasElement': Tainted canvases may not be exported.} 

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available