This question of yours is extremely non-specific, as in you never measured which part of the synthesis you notice loss in total yield.
Also, let's not forget that if you want clean, alpha of the alpha-pvp's you will have to no matter what purify & crystallize & then re-crystallize till you start pulling your own hair out of anger, to the point where the alpha-pvp is at a level that will satisfy your or your clients needs, as depending on their road of administration, if the product is not clean enough they will be angerful about the taste if vaporized, the causticity if intraveniously administered, or insufflated.
Applying the upper mentioned, try to make some calculations and note them down too with each step in your procedure, then try to see if there is any problems, and don't forget to purify it.