Just curious: Do you have your DipTrace graphics mode set to Open GL? I don't know if this is related, but I'm am seeing a slight offset (bottom/right sides rotated towards viewer) in the 3D Preview tool after using the Reset View button. It seems to me that the precision should be limited to maybe 3 decimal places when using metric and maybe 4 places when imperial units are used. I'm curious if anyone else is experiencing similar issues? For example, a number I presume to be 3.8 is represented at 3.79999999.) I don't have any knowledge on the organization of STEP files but I did open the file associated with this particular board and noticed that some of the data points are carried out to several decimal points. Trying to line up surfaces that are part of the imported PCB results in an angular misalignment of fractions of a degree but it is enough to thwart SolidWork's effort to properly align the parts (see image). Overall the process works well except that component surfaces that are part of the exported STEP file are not parallel/perpendicular to each other. These files are then imported into SolidWorks and inserted into whatever assembly the PCB is a part of. I regularly export PCB layouts from DipTrace using STEP files.

Diptrace to solid works