Which version of Windows are you using? Also, are you using the new DisplayFusion 8.1.1?

https://www.displayfusion.com/Download/

Thanks! We were able to reproduce this issue here, and I've added it to our list. We'll be sure to let you know as soon as we're able to fix it up

In the meantime, as a workaround, if you choose the "Different image on each monitor" option, then pick the same video for each monitor, it should work correctly. (at least, that worked for me)