Hi Malorie!
First, I think it would be helpful to consider what impressions and engagements are. Impressions measure the number of times a post appeared in users’ feeds while engagements measure the number of unique people who've clicked, liked, commented on or shared a post.
When your impressions are up and your engagements are down, it could mean that while you are reaching a wider audience, the posts are resonating with them less (hence the lower engagement). If engagement is high but impressions are lower, it could mean that although less people have seen your posts, the ones who do are perhaps more of a targeted audience that is likely to interact with your content.
I wouldn’t classify having impressions go up while engagement decreases as necessarily a bad thing (and vice versa). It really depends on what the goal of your efforts are. For example, if you want to reach as many people as possible, then higher impressions are great. If you’d like to curate an engaged base, then higher engagements could be better. You can monitor both of these metrics (and more) to understand how your content impacts your audience.
Also! If you recently ran a paid campaign or used funds to get an organic post in front of a wider audience, it could also explain the increase in impressions.
I hope this was helpful!