Ok weird issue with Diesel

So my issue is that when I take Diesel out in the morning and afternoon (right up until about 5:00pm) he has fine, healthy poops but after that they become really liquid-y/diarrhea-y. I can't commit to it being his food (I feed him natural balance) because it isn't constant but I don't know what else it could be. I feed him roughly the same amount twice a day (he might get a little more depending on how much ends up in the scoop but he only gets 1 cup-ish plus a little wet food), but have just recently started to include some wet food in both of his feedings to get him to eat all of his food at once rather than grazing like he does if it is just kibble.

Does anyone know what could be causing evening/late afternoon diarrhea in a 4 1/2 month old puppy?

Separation anxiety? If you are walking him in the morning and his poops are fine, then you go to work or w/e and come home and he has diarrhea it may be from separation anxiety.

I could see that except it happens even if I am home all day with him. Yesterday we spent the whole day together and even went to the dog park and a walk so I don't think it is separation anxiety. But that is a good point, it might contribute to it on the days I do go to work.

When is he getting the wet food? In the evening?

My aints lab pubby gets runny poops when she eats wet wellness.

He's getting the wet food in both the morning and the evening, and not a lot, just 1/4 of a cup so that he is tricked into eating all his food at once (and plus I've heard that the wet food has more nutrients in it anyway).