Yes, a video is really only a moving picture, so still has all of the same disadvantages. There is a reason why we ask for a project file to be attached and not a picture or a video (or a rough pencil drawing, or a 100 word description, or an excerpt of an audio book, etc…) – it’s because we can quickly diagnose problems from Dorico projects and we have to guess with everything else. The absolute best thing you can do is what you have done in your most recent reply, and as I asked you to in my original reply: copy and paste a tiny bit of the music to another project so you have a minimal case to reproduce the problem, then attach that. It really, really helps.
Now, the answer to your original question:
When Dorico imports a MusicXML file, it does so in such a way that properties that would normally be set on a per-layout basis get set globally, i.e. the value will apply to all layouts. The Properties panel expects each property to be set with only a single scope, which is defined internally in the software. However, many properties can technically be set with a different scope, though not from the user interface as it stands. (This is why we currently require Edit > Propagate Properties.)
When Dorico encounters a dynamic with forced placement in a MusicXML file, it sets the ‘Placement’ property. But no layouts exist at that point, so Dorico sets the property for all layouts. The Properties panel doesn’t know how to handle this: it can tell the property is set, so it’s shown as activated, but when you try to switch it off, its rules for how it expects to be able to determine the scope of the property are violated, so it doesn’t work.
To work around this, you should do Edit > Reset Position on the dynamic, which will clear this “global” property and allow you to set it on a per-layout basis as usual once more.