Open rates dropped from 40% to 6% with no changes on our end. Anyone else experiencing the same?

We have consistently had 40% open rates until the end of August when our emails are being delivered straight to SPAM for most, and we only have a 6% open rate. We went ahead activated the DKIM key for self authentication, however we had a high open rate without activating it so I know that is not the root cause of the issue.