Tummy tuck & Internal corset stitching, resulting in what looks like a Hernia. Is this possible?

If you have a 'hernia' like protrusion, you should speak to your surgeon and perhaps get an ultrasound or a CT to see what's going on.  Each surgeon does the muscle repair differently.  If a continuous suture was used, it is unlikely that you would have a hernia-like protrusion, as the entire repair would come apart.  If your surgeon used individuals sutures, and one broke, you would have some loosening of the abdominal wall but again not a 'hernia'.  Further investigations may be needed.

Plicating the muscles (internal corset) pulls the overlying tissue with it creating a bulge in the upper abdomen and if not spread out adequately will create a bulge.  If you do a crunch and the bulge worsens, you have a weakness of that area.  If you had a mini-tuck, this could be a reflection of not having the upper abdominal muscles sutured.  If you had a full tuck, then your sutures may have failed or your tissue stretched out but this means you were flat after surgery and this bulge then developed.

It is possible that the stitches have given way in the upper half, or that the stitch line did not go high enough (not as likely).  You will need to see your surgeon of course to decide what to do.