Incomplete evacuation is a symptom of pouchitis. I did have a septum develop in my pouch in the late 1990s and it produced a completely different sensation of the stool hitting a wall. I knew there was a physical problem there was no guessing. This was later confirmed and the issue was resolved surgically with a revision of the J pouch.
It also could be a stricture as previously suggested.
If the usual pouchitis treatments don't work you should probably see your surgeon.