I am attaching the requested images
There is indeed something wrong in the way the model constrains where defined for the right hemisphere, but I can't guess what from this limited information.
but of course the lead field vectors are not shown properly
If you want to be able to see something, you should increase the size of the arrows.
But these representations are difficult to understand if you are not very familiar with the question of forward modeling.
I had seen the warnings with the mixed model, but there are two observations based on which I have still preferred using it:
I think this warning is clear eanough: " Mixed head models are mostly indicated for individual subject analysis, and not suitable for group analysis when using individual anatomy for all the subjects".
In the context of group studies: don't use these mixed models.
I strongly recommend you use simpler models: surface or volume.