Internal user account flagged as "External"

Hello rbgibbons 

welcome to the Microsoft community, my name is Recep I'll be happy to help you today.

I understand that you have internal users flagged as External in Teams, to narrow down the issue, please check the few things:
1. Make sure you disable Firewall, Antivirus, VPN/Proxy & Adblocker for a while for troubleshooting purpose.
Follow the below steps to disable Proxy on Windows 10: Click on Start, select Settings, and navigate Network & Internet > Proxy.
a. Toggle the option Automatically detect settings to ON.
b. Toggle the option Use a proxy server to OFF

2. Disconnect any external device, e.g. Monitor, camera, headphone, dock station etc.
3. clear cached MS Teams login password from credentials manager:
a. Open the Credentials Manager (Control Panel > User Accounts > Credential Manager)
b. Select Windows Credentials
c. Under Generic Credentials, you will see one called: msteams_adalsso/adal_context_segments.
Also, any credentials entry related to MS Teams and Office.
d. Delete them all
e. Follow step 3-4 for Web Credentials
f. Sign out and Sign-in again
g. Try accessing Ms teams app again

3. Reinstall the MS teams app https://www.microsoft.com/en-sg/microsoft-365/m... and try again.

For MS Teams web app, please clear browser cache and cookies for all time and try again:
https://support.google.com/accounts/answer/32050?co=GENIE.Platform%3DDesktop&hl=en