itsafulltimejob

Hi I'm very new to 3d printing but learning as fast as I can. I'm also new to forums so sorry if this is not in the right place. I have an Ender 5 and printed quite a few parts fine with Creality slicer. The only problem seemed to be the supports which would not work at all. I have now been trying Ultimaker latest version which prints the supports well and does the job, unfortunately on each print I have tried, it misses the studs off of the top of the object and clicking on preview shows them grey. I have tried fixing the stl on different sites etc but none show any errors after the first fix in Freecad. Can someone please tell me what is wrong because Creality slicer prints the studs. Thanks