Just after engine shutdown on the CFM56-7B, smoke comes out of the tailpipe, as seen on the video. This is a very normal behaviour of this engine, and it stops after a few minutes. It is oil and/or oil/air leftovers which contact the hot engine exhaust and tailpipe hardware causing the smoke. Since there is no active airflow and/or sump-return functioning when the engine is stopped, the oil fumes and smoke are visible and only moved by the wind. If the engine is running or there is a strong wind, you do not see this smoke and therefore are not triggered on the precense of the smoke. Just ignore it, avoid it (it is not healthy as you may expect) and leave it as it is. It will stop and dissappear automatically.
> FOR INFORMATION ONLY. UNCONTROLLED DATA !.