>>58704 Aight gents. I think it's down to the file format. The original uses the QT file format (major_brand qt), while both my libx265 transcode and simple remux change it to ISO base media format (major_brand isom). So, in other words, a simple remux "fixes" the thumbnail issue. It uses practically no additional resources and can be done instantly even on potatoes (annoying nonetheless). Example remux:
