Sylvia Seeing half of what you expected might be caused by having a Joint savings account with 2 people, as each member received interest over their own (equal) share of the money that is in it. Other reasons for seeing other values as expected might be calculating with the wrong interest rate (for example there's a promo for residents of Germany in the first 4 months to receive 2.55% interest p.a., but you might be a new user from Denmark getting only 1.56% interest p.a. currently), or other types of calculation errors.
If you want to share more information and get an explanation on your specific case, you can either do so here (keep in mind this is a public forum) or just contact bunq Support to help your privately. What I haven't seen so far are any actual errors made in calculating interest payments on the bunq side, but of course it's always a good idea to double-check by yourself.