There are a few ways to report a bug or any problem you may be having with Microsoft Pix.
1) In the upper right corner the Microsoft Pix Help Desk you'll find a "Submit a request" link that you can use to contact us regarding any problems you might have with Microsoft Pix. There is a Feedback field and a link for attaching any files or screen shots that you think might help us provide a solution.
2) You can also provide feedback directly through the Microsoft Pix app. Simply go to the Gallery, click on the menu icon in the upper left corner, and select Feedback. Enter your email address, report the bug or problem your having, and hit "Submit".
3) You can also Submit a request here.