Injuries robbed Lewis - he hasn't looked comfortable at the plate since 2023. Whatever changes he made to his stance and mechanics - obviously not working and I think he's in his own head right now.
Nothing to be gained by Wallner being in the line-up. His confidence is gone. He's not going to suddenly run into a hot streak. Send him down, let him get right (hopefully) against minor league pitching and re-evaluate in a couple of weeks.