Video error - I change the video description and it becomes audio only

Hi!
I have uploaded a video to SharePoint for my colleagues, and if I don't change any information, such as the title, description, adding a thumbnail or subtitles, the video works perfectly. However, when I try to modify any of this information, Stream displays it as an audio track, with a still image (the thumbnail) on the video preview. To trick the issue i had to upload a blank empty png thumbnail that allows to shows the video behind. Im' not so happy about it.
How can I solve this issue?
Ironically, if I download the MP4 video from SharePoint, it opens as a video, as it should be.
Thanks for the advices!
Giovanni