If you're seeing more mail in spam filters, there's a host of things that may be going on. I would first recommend verifying that you are using the technical settings for deliverability, SPF & DKIM, and branded tracking links. If you're missing any of those, you might want to set them up.
Do you use a deliverability testing service such as the IBM deliverability tool from our Deliverability PowerPack? If not, I would recommend investigating one of these services. You can send your email to a number of addresses owned by the testing service at a number of different providers. The service will then tell you if the message goes into the inbox or junk folder, which can be very helpful.
For more assistance, contact the support team. We have deliverability experts in the support team who can assist you with troubleshooting issues like this. If they aren't able to help, they can also escalate the matter up to the Privacy Team for more in-depth assistance.