Cannot have 3 TVs on Directv

If you're on a grandfathered plan, then more than 2 streams won't work in-home.
Check https://www.directv.com/support/article/000079946

Grandfathered Accounts: Older legacy accounts (such as those that started as DIRECTV NOW or AT&T TV NOW) do not get unlimited streams and are generally capped at 2 to 3 concurrent streams total, regardless of location

Did you replace a Firestick? (old one may still be registered)

Did your login info get shared with anyone? (in case your account is being used)

Shared your WiFi details? (perhaps someone on their own account is accidently connecting to your WiFi causing it to count as a 4th on yours in error).

Since it is at home, I would consider rebooting your Gateway (modem/router combo) and/or changing login details (both Gateway and your DIRECTV STREAM account). That would hopefully kick off any additional device that may be connected or cached in memory and prevent it from connecting again (provided you don't share any of those login details).

Thanks for following up with us on the recurring streaming limit issue, @jeflehman. We have a technical specialist ready to assist. Sending you a DM now. John, DIRECTV Community Team

Thanks for your help.  It's much appreciated!  I am on a grandfathered account so I added another stream for $5.  Interesting that the DirecTV Customer Support agents never offered this solution.

Glad that we fixed the streaming limit issue. Sorry that the add-on wasn't suggested right away during your call. Enjoy streaming and contact us here if you need anything else: DIRECTV Customer Service - Phone Support & Chat. Charles, DIRECTV Community Team