why i am seeing the purple window?

Do you mean something like this?

The purple underlay is a debugging feature that can be triggered manually or automatically when a layout error occurs. I deliberately mangled the layout of this sample app.

To disable the most likely trigger of the issue (this won't correct the layout problem—it'll just stop the underlay from showing), you can paste the following command into Terminal and then quit and reopen Photos:

defaults delete com.apple.Photos NSConstraintBasedLayoutVisualizeMutuallyExclusiveConstraints

If that doesn't keep the purple window from appearing, then it's being triggered manually deep within Photos's source code and there's nothing you or I could do to directly stop it from happening.