Greetings,
Do all domains share the same DKIM key? They look the same.
Thanks in advance for shedding light on my ignorance 
Are you perhaps have multiple domain on cPanel? If yes then this tutorial will help (altough you can access it directly from your cPanel): https://io.bikegremlin.com/11200/mxroute-email/
You may go to section 5.1 DKIM DNS Setup
They are not. Make sure you’re choosing the domain in the dropdown menu at the top. The differences may be subtle.