Unfortunately virtually all foods have a limited number of people allergic to them. The UK and EU list 14 categories of allergens which are relatively common, flaxseed is not one of them. https://www.food.gov.uk/sites/default/files/top-allergy-types.pdf
I’ve just checked this page and they say that flaxseed is not a “commonly involved in PFS reactions” - https://www.allergyuk.org/oral-allergy-syndrome/oral-allergy-syndrome
Having said that we are aware of the flaxseed allergy and we are sorry but to remove all potential allergens is impossible, there are simply too many. For example, I had no idea until recently that people are allergic to apple, banana, figs, etc, etc, and that is just fruit. http://www.foodallergens.info/Allergenic_Foods/Fruit.html