Zepplin file uploads displaying with transparent background in pop-up

[Deleted user]

I have integrated a Zepplin account with our Jira account successfully. 

When I attach a Zepplin file, originally from Sketch, the file pop up in the Jira issue card is displayed with a transparent background in png. The file I am attaching is a wireframe. 

This issue does not occur when I am in the Zepplin app or web-app. The wireframe file in sketch has not got a transparent background so I'm not sure what could be causing this other than an issue with the Jira/Zeplin integration.

Please let me know if there are any settings for this or if the issue is due to a bug with Jira. 

In Jira:

 

Same file in In Zeplin web app: 

Thanks in advance, 

Maria-Elena