I had imported a illustrator file, then extruded, then I had applied the Poly bevel node but I had encountered several issues, can someone please take a look at the capture provided?.
Hard to tell without having a look to the real geometry.
As you don't provide an explicit edge group, did you use the exclusion option (ignore flat edge) + angle (around 30 probably). You might want to compute the normals after the bevel (vertex - by face area for the weighting) to get good result with ngones. (even tho it's not your initial problem here).
you can see the very elongated and superthin triangle in your body - it will cause problems for polybevel (otherwise it will result in broken geometry if bevel overshoots them)
Also make sure that your AI curve is clean. Illustrator files might contain curve points too close together or even self intersecting curves. I'd resample the curve first in any case.