The nutritional needs of deer are different at different times of the year. We now know that there are three different periods of a deers nutritional cycle. The sodium/potassium needs are higher during the "Green up" period than at the rest of the year. During the green up period the bucks are growing their antlers and does are lactating. In this time period the salt intake increases to about 14-18 percent of TDN.The protein intake is greatly increased also. Doe's require about 150% more protein during the lactate period than the rest of the year. At about the time of the pre-rut the animals start to slow in the antler/lactate area and starting to "bulk up" with protein. It is not unusual for deer to stop/reduce using licks and start hitting the alfalfa and clover fields, while during the mid summer they may have stopped/reduced using the forage fields amongst the other types of available nutritional products vailable, to search for other needs in their diets.
Another thing is, the types of clover/alfalfa/forage may be bitter during different times of the year, ergo the custom blends. Also, maybe mow to increase new growth. Taste the forage product. If it is bitter try limeing...
The licks should resume heavy usage after the start of the following green up season.

Romans 10:9 Psalms 42