Coconut Cookies have bitter underlying taste
Baking requires accurate measurements. In fact most people who bake seriously avoid volume measurements for anything but liquids, and use weight instead (with the exception of small quantities up to about a tablespoon, which affordable scales have only been able to measure accurately in recent years. 

That said, there aren't any particularly bitter ingredients, except the baking soda, and you say the rise wasn't good. However baking soda needs to react with acid, and a shortage of acid would lead to both a poor rise and a bitter flavour. Coconut and butter are both slightly acidic, and even poor mixing  of the soda and acid can cause bitterness and a poor rise