Troubleshooting Newsletter Delivery: Stuck in Promotions?

I've been running my newsletters for 4+ years now. I ask readers to engage (click links, reply, and drag to primary if they find the email in promotions/social/spam/etc.) I also do this every time I see an email in my own inbox. For 4+ years I've always hit the primary inbox (hopefully in part due to these actions). Lately however they keep going to promotions/social. Even in my inbox when I dragged it to primary the day before. Been dealing with this for a few weeks now, not sure if anyone else has had this issue and might have a suggestion on how to fix it. My open rate has definitely taken a hit.