Thank you for reaching out to the Community! I can definitely understand how important it is to keep your email engagement high. I would be happy to help take a look with you. When testing one of your latest campaigns it landed in my Spam Inbox. Emails landing in Spam can trigger a decrease in your engagement.
In fact, I was able to notice there are a lot of 3rd party links in your campaigns. One of those could have a bad rep that causes the email to go to spam. Because of this, I would suggest calling into our Deliverability Department. These support agents can help troubleshoot this further for you.