I just fixed a bug in this action that may have been causing this issue.
Can you please update the action (you can do this by right clicking the Instagram Downloader action in the Dropzone grid, clicking edit and then clicking the 'Check for Action Update' button) and then trying this download again.
Make sure the Instagram Downloader action is on version 1.2 (this is also shown when editing the action).
If it still fails, can you please also provide the Instagram post URL you dropped on Dropzone that failed. This is also included in the earlier section of the debug log but you haven't included this above.