Thank you for the query.
It can be something left under the skin indeed. But it is really hard to leave Trocar tube under the skin. It is not even hard, it is impossible. You never put whole Trocar inside, the largest part always stays outside the skin. So trocar tube sounds really impossible.
If this tube object is soft, most probable is hernia (fatty tissue from the abdomen more precisely) in the scar area. Inflammation always makes wound healing
very hard. Appendix
is usually infected so during taking it out, the wound gets infected as well. This makes this point weak and prone to hernia appearance.
The best way to find out what it is, is an ultrasound
of this are. Please ask your doctor to perform this test.
Hope this will help. Feel free to ask further questions.