Its hard to really comment without a vid of some sparring so we can see what your refering too, from what i understand it sounds like it could just be a lack of confidence in mid range could be the problem, or maybe hes had bad experiences with the positions hes being caught in there before and this is causing hesitations.
fear of the unknown, knowledge and ring experience will nurture that, so many different factors might be involved, footwork.. it could be poor and may be tieing him up limiting his options at times where your noticing due to the way hes using his feet to evade shots close and long range could be leaving him exposed and/or unable to throw shots at times midrange, it could be so many things.

To be fair what i figure by your descriptions it sounds like the guy is doing ok as he is, hes always learning while hes active and im not sure about your experience in boxing yourself so let me say its not as easy as it looks, to stay elusive long, mid and close range while hammering in tidy combo's in a controlled manner as not to compromise balance and mobility at any point in the sequence is quite an art, maybe your expecting too much from him too early? if he didnt have a big amature career? then again maybe the sparring is of quality that you feel he should be dominating at this stage and your seeing he isnt? we dont know, like i said videos will help us help him.