This question is underspecified. I am assuming that a lot of your DICOM files are not DICOM images. For example, other patient records stored in DICOM files. You may want to rename your DICOM files to get a better idea of what you are working with, e.g. "dcm2niix -r y -o ~/renamedDICOMs ~/inputDICOMs'. My sense is that this needs visual inspection, but is likely the expected output for a complicated set of DICOM files. You might want to use the '-i y' to ignore some of the 2D planning slices. 

For future Siemens acquisitions, I would heed the warning from the manufacturer "Do not use the mode H>>F because this complicates the numbering and you will have to sort images manually in most fMRI post-processing tools."

https://www.magnetomworld.siemens-healthineers.com/clinical-corner/application-tips/slice-order-fmri.html

https://crnl.readthedocs.io/stc/index.html