We are dealing with the decisions of real people. After each giveaway a percentage of users will unfollow you. That and natural Instagram follower loss is a real thing when monitoring the growth of your Instagram account. With this in mind, don’t immediately look at your new, high follower count at the peak of the giveaway. Ignore your follow count for a few days and just focus on posting some more content- at the end of this period, check your followers again to find out just how many stayed because they liked what you were doing with your page.
We also highly suggest you participate in multiple giveaways to really see the benefits.