Possible reasons for missing images....
If they are missing from the beginning of the roll.... film not wound on far enough at the start.
If they are missing from the end of the roll..... film wound on too far at the start.
Are any frames double exposed?..... film either did not wind on when you re-cocked the shutter or double-exposure lever activated.
Blank frames in middle of roll....... could the dark slide have been in place while you were taking the missing shots? I know you are not supposed to be able to fire the shutter with the dark slide in, but I used Bronica SQA's and if you pulled the dark slide by as little as ½mm, the shutter would fire but obviously nothing was recorded on the film.