What would cause hardness where the sutures were after Tummy Tuck with Lipo?

Dissolving sutures are usually gone by three months, and the return of an abscess may be related to an area of fat necrosis along the suture line which became contaminated during the upset with the sutures. Fat necrosis is an area of dead fat where caught in the sutures. After drainage and control of the infection, the stiffness can persist for a long time, several months. If the hardness is spreading let your surgeon see you right away to confirm the infection is indeed gone.
Best of luck,
peterejohnsonmd

When a wound is allowed to heal in over time, this generates a significant amount of scar tissue. This process (termed "closure by secondary intention") prevents the re-accumulation of fluid or blood which can lead to another abscess. Once the skin has healed, it is not uncommon for the area to feel quite firm. This generally improves, but can take over a year until it has stopped softening.

It sounds like this is nothing more than some scar tissue left over from when the wound opened and it shoukld go down in several months.