The configuration settings on your server would not change due to an Internet outage. However, something might need to be reset or restarted.
Any other remote users? Are they having access issues as well? Alternately, try accessing via your phone & the mobile network or from another wifi network. This is just to check and make sure your sister’s network is not the issue (your other post mentions you are at your sister’s place).
Can you see your server via Plex Web, https://app.plex.tv/desktop?
If so, what is shown for Settings -> Remote Access? Fully Accessible or Not Accessible?
Note your public IP address & remote access port number. Verify connectivity using an online port check tool such as https://www.yougetsignal.com/tools/open-ports/, using the public IP address & port of your Plex server.
Monitor playback using Plex Dashboard -> Now Playing? Does the connection show as remote or indirect?
If indirect, it means you are connecting via Plex Relay, which is bandwidth limited, not via Remote Access.
Possible corrective actions:
Because it is easiest and you are there, reboot the Internet modem/router/etc at your sister’s place. Once it is back online, reboot the devices you’re using to access Plex (TV, iPad, etc).
If possible, configure the devices to use a public DNS server such as Google, 8.8.8.8, or Cloudflare, 1.1.1.1.
Is anybody available in Atlanta to restart your equipment? If so, start with the AT&T modem/router/gateway and work out to your Plex server, including any additional access points, switches, etc along the path. Then recheck status via Remote Access settings and the port scanner.
