https://graph.microsoft.com/beta/security/alerts started returning error

Last week I've started this thread https://techcommunity.microsoft.com/t5/Using-Microsoft-Graph-Security/https-graph-microsoft-com-beta-security-alerts-Not-returning-any/m-p/191898#M5

The issue was identified and solved by Microsoft, but today were now getting an error, both from graph explorer and our applications, in both of our tenants:

{
"error": {
"code": "UnknownError",
"message": "{\"@odata.context\":\"https://isg-prod-eu.trafficmanager.net/security/$metadata#Edm.String\",\"value\":\"Auth token is not for ISG audience. Please see document at https://techcommunity.microsoft.com/t5/Using-Microsoft-Graph-Security/Authorization-and-Microsoft-Graph-Security-API/m-p/184376\"}",
"innerError": {
"request-id": "bc0b6133-3e79-40c7-8bf4-b49c55bc3d35",
"date": "2018-05-15T07:37:01"
}
}
}