I think the video is self explanatory. What gives?
Is this project from an XML by any chance?
Can you please upload it - or that portion of it.
There is something tricky going on lately with 4/4 meters imported from XML. The double barline is in fact a hidden meter (as always in Dorico). So deleting and remaking the double barline should be as good as inserting a new meter.
See this thread for more discussion: