I am reasonably sure it is a video editor problem but you can try again. When you export your image as a png untick all the options as: https://i.imgur.com/Z0zAz4N.jpg
Probably not going to make any difference, try an alternative video editor, for simplicity Avidemux will overlay a logo into a video. example: https://i.imgur.com/d6z5yXL.jpg There are versions for both Windows and linux. Looks like this. Works ok here, no borders on playback.
I do not use Instagram (or social anything ) so I can not comment on how they render video.
Probably not going to make any difference, try an alternative video editor, for simplicity Avidemux will overlay a logo into a video. example: https://i.imgur.com/d6z5yXL.jpg There are versions for both Windows and linux. Looks like this. Works ok here, no borders on playback.
I do not use Instagram (or social anything ) so I can not comment on how they render video.