When I import a STEP file PCB assembly several components disappear when I save it. Also it complains of empty sketches, dozens of them, asking me to delete them during the save.
If I choose 'Yes' and delete them some parts are missing.
Should I choose 'No', and save the assembly without deleting the empty sketches, virtually the all the parts disappear.
If I open the STEP in E-Drawing no problems are seen. Every part is visible.
..could be your template(s)? (unsaved sketch?)
..try a test.. open a simple assembly and saveas STEP.. now open that STEP... same problems?... if so.. your templates may have a unsaved sketch?