With different file formats to import to IRONCAD comes different needs and you might have to change some settings when importing a model, in order to get the best possible result. STEP files are "neutral", which means that the active solid kernel (ACIS or Parasolid) in IRONCAD will read and create the model in the way it best finds suited. Sometimes you might have to change the active solid kernel in IRONCAD and redo the import of the same file again. It can also be worth changing the active kernel afterwards, in case the model still have topological problems where faces/edges/vertices are not holding together.
If you import an ACIS (*.sat or *.sab) file it will always use the ACIS kernel in IRONCAD, even if Parasolid is set as the default kernel and the other way around with a Parasolid (*.x_t or *.x_b) file.