I am not sure what to do to troubleshoot further:
I did recently move my domain to CloudFlare (but I have always used CF DNS) but I did that on March 8th and my last email was April 9th.
I have used https://toolbox.googleapps.com/apps/checkmx/ which came back all fine except DKIM / DMARC / SPF which have never been set up properly. So Google sees the DNS pointing to it properly.
I'm not sure what to do or what to troubleshoot next?