You may want to add a week where you drop the weight to 80% of max and rep out as many as you can. Giving your muscles a break from PB lifting and changing the strain on them can increase gains. After a week of higher rep work, go back and see where you are. It also could be as simple as deitary or sleep related. Small changes can have real effects on your lifting.
It sounds like you are on a golden 5 cycle, You didnt mention pull ups, but I would assume you are on Squats, Deads, Bench, Military Press and Pull ups rotation. You could shift those to front squats and romanian deads for legs, sumo deadlifts, dumbell incline bench, clean and press and weighted negative pull ups for a few weeks and see if that breaks your plateau/ loss.
Finally, I am not big on supplements, but creatine is a game changer. I stay away from protein drinks as they"re a lot of ingredients I dont want added to the few I do want. Eating clean protein and greens with clean carbs will give you all you need. Besides, who wants to get big or change shape dramatically? I couldnt afford the alterations!
Feel free to PM me if you want to discuss any other specifcs about your situation or potential remedies.