Jordan
I have seen this you need to make sure that your appid is correct in the signininfo.json file in the server directory of the web appbuilder. Update this and it should work correctly. Also you want to make sure that your computer name or IP has not changed on the development machine you are using.
[
{
"portalUrl": "https://magic.maps.arcgis.com",
"appId": "xxxxxxxxxxxxxxxxxxxxx",
"supportsOAuth": true,
"isWebTier": false
}
]