Facebook ads, when performing well at first will eventually go through what we call Facebook Ad Fatigue. This happens when your campaign frequency gets too high – people are seeing the same ad from you to many times – and those people become less responsive to your ad. When that happens, your previously well-performing ad no longer performs. To combat this, keep a watchful eye on your ads and change up your ad creative and/or your ad copy.
Actively Manage Your Facebook Ads