If you have no contraindications, then no. As mentioned above, there are a lot of carbohydrates and starch. Therefore, diabetics and people for whom carbohydrates are contraindicated (in particular to me), it should be excluded or severely limited. In principle, if it was in the package, then it is impossible to mix anything there. Sometimes lumps of earth (very small) come across in cheap cereals, but for this, the housewives usually wash it and sometimes soak it overnight like rice. Buckwheat is absolutely impossible to poison.
Buckwheat is not a perfect product. For all its advantages (the mass of amino acids, a lot of proteins and a scanty amount of carbohydrates), it has disadvantages, especially if consumed too often. Buckwheat contains a lot of starch, which causes discomfort in the stomach and irritates the stomach. There is an excess of fiber in cereals, there is so much of it that in case of an "overdose" you are guaranteed problems with stool. In addition, it is a strong allergen; in the past, its use was even limited to pregnant and lactating women. Well, do not forget that there are very few vitamins in buckwheat, so it should not form the basis of human nutrition, and I do not recommend keeping the buckwheat diet longer than 5-7 days.