Notes:After recording @ 1920 x 1080, my video shows at half resolution vertically but full resolution horizontally, with the recording showing in the bottom half of the screen and all black above.
As a newcomer I am only allowed to upload one file, so I’ve stitched the two screen dumps together. The top half is the original, the bottom what showed in the editor.
Maybe you accidentally resized the video object.
Please right-click the video, select Restore Original Size and set its Left/Top (in Properties > Size & Properties tab > Transform section) to 0/0.