As per the link Stuart Lodge's comment, the problem is due to the linker not including the reflected property referenced in the MvxBind expression.
I added a class with an explicit reference to the property to force inclusion by the linker, now all is well with my Release build!
internal class LinkerForceInclude
{
private LinkerForceInclude()
{
}
private void IncludeChecked(ToggleButton button)
{
button.Checked = !button.Checked;
}
}