I dont think it's mental.
Its not like 2015/16. Then, we'd go ahead, soil ourselves, drop deep and not press the ball at all. Even when we go ahead in games under Lowe, I think our shape is OK.
However, I wonder if it's a fitness thing. I dont mean this in a "we need to much fitter" type thing, but this system requires us to be so fluid in possession and energetic off it. When we're on it, as we were in the first 35 tonight, we're brilliant. But it does require a lot of energy.
In our bad spells, we just seem to go quite static off the ball and struggle to retain it for any length of time. Its a circumstance of our style playing out from the back. We need to persist with the style in general, its the best fit for this squad, but maybe acknowledge when the passing game stops working as well, sacrifice a CM, go to 3-4-3 and play it longer into the channels more. It will stop us from coming under so much pressure in 2nd halves.