My little sully sometimes eat his eco earth substrate. Especially when it's fresh. I haven't seen him eat is own poo. But it seems like it's normal. I wouldn't worry about it
There is a lot of good fiber and other nutrients left in there, because they do not process all the nutrients out of it the first time through. One of mine does it more than the other one, I just try and pick them up before she can get to them.