Black Frame after Exporting Video

Hello forum,
when I want to export a video, the encoded video file has a black frame at the end. I encode with different clips that have different resolutions, i.e. 3840x2160 and 1920x1080. The codecs are also different: HEVC and H.264. Everything looks just fine in the preview before it’s exported. Then, when I export it in 16: 9 and 3840x2160, the result has a black frame. Please, what am I doing wrong? Thanks for the answers.

In my experience, Shotcut can sometimes have difficulties when combining clips with differing encodings.

I would suggest converting everything to one edit-friendly encoding, using either the “Convert” button in Properties or using Export incorporating your own favorite parameters. (There are loss-free codecs available for this, if this is needed.)
The do then editing with clips that are now all encoded the same.