Cannot use specific icloud alias email address in iMessage

One of my icloud aliases is really the main email address I use for corresponding with anyone. That email address has always shown up as a checkable option to use alongside my cell phone number for iMessage along with a handful of other aliases. But now it's not showing up on any of my iOS devices or Macs anymore in iMessage and I have no idea why.

I signed in to manage my apple ID in a browser and saw that I could add an email address to the "reachable" list for iMessage, FaceTime, etc. So I manually tried to add it, the system sent an authentication code email to me, I entered the code, and it came back multiple attempts with an error and just said I couldn't use that email address with iMessage.

I thought I'd ask the question on here first before calling Apple to see if they need to intervene.

Anyone know if anything I can do to fix it on my own?