Thanks for the suggestion about adding the small amount of corn syrup. I will give it a try. When this problem with crystalization occured, I sent an email to my maple syrup supplier, giving him all the info about it. I asked him if he had any suggestions and I just received the following reply:
First, we can do it with maple syrup only. My mom is doing it. But, we must use a low inverted saccharose sugar!!!! Maple syrup, fresh made is high in Saccharose sugar. When it become older, the saccharose sugar invert to Glucose and Fructose sugar and it is difficult to make chrystalization.
The maple sugar was made when the Saccharose sugar was at high level = Reason of Chrystalization.
Second: on your mixture, did you cook the maple syrup and the maple sugar together? You might cook it up to 252 F and more. Maple sugar is cooked up to 258 F. but it is lower than 4 % of moisture. After, put on oven for drying..
Third: I'm suggesting to use 3 parts of sugar with 1 part of maple syrup, melt the maple sugar with the maple syrup, cook it up to 254 F. mix with your nuts and dry them on oven (150F for several minutes). Why 3 parts of sugar and 1 part of maple syrup - The maple sugar is on christalized texture. Either the maple syrup is on inverted sugar, the mixture will chrystalize...