If you reimport the file on export, and view the exported file within Premiere, does it show as it should?
A screen grab of your program monitor showing the transition within Premiere, a screengrab of the export dialog box showing your export options, and one of the video re-imported into Premiere would be ever so useful.
Simply drag/drop the image files onto your text reply box so they appear directly in your post ... do NOT 'attach' them.
Which version? The latest? If so, are any of your panels floating? Try using one of the dedicated workspaces, not a custom one. If that's not the issue, try deleting Premiere Pro preferences. Still not working? Try Project Settings > General > and set GPU acceleration to Software Only.