A decrease in Gmail open and click rates after fixing DKIM, despite passing SPF, is a multifaceted issue with causes extending beyond basic authentication. Key factors include a potentially damaged sender reputation (possibly predating the DKIM fix), content quality, list hygiene, user engagement, and changes in how mailbox providers perceive your email stream. Mailbox providers like Google use various data points, including AdWords and Search Console data, to assess domain reputation. Sudden changes in sending patterns, spam trigger words, and overall user engagement can also negatively impact deliverability. Gradual warming of IP addresses and domains after significant changes is essential, as is A/B testing to optimize email content and engagement. Furthermore, it may be due to Google's GPT reporting less data due to the low sender reputation.