I was having this same issue while trying to bind to a command on my view model.
I changed it to use a relative source binding rather than referring to the element by name and that did the trick. Parameter binding didn’t change.
Old Code:
Command="{Binding DataContext.MyCommand, ElementName=myWindow}"
New Code:
Command="{Binding DataContext.MyCommand, RelativeSource={RelativeSource AncestorType=Views:MyView}}"
Update: I just came across this issue without using ElementName, I’m binding to a command on my view model and my data context of the button is my view model. In this case I had to simply move the CommandParameter attribute before the Command attribute in the Button declaration (in XAML).
CommandParameter="{Binding Groups}"
Command="{Binding StartCommand}"