Azure Data Factory Scheduled Triggers Not Working

I tried to setup scheduled triggers within Azure Data Factory, but they are not getting executed and are not logged either. They used to work but since a couple of days nothing happens anymore, even when I delete them and setup new ones.

When I hit "trigger now", everything is fine. So basically I setup scheduled triggers (activate them), deploy them and wait for the automatic call but nothing happens at all.

Do you have an idea?

lot of configured triggers emtpy trigger execution logging

eg:

{
"name": "Trigger_Hourly3",
"properties": {
    "annotations": [],
    "runtimeState": "Started",
    "pipelines": [
        {
            "pipelineReference": {
                "referenceName": "Pipe_02_xy",
                "type": "PipelineReference"
            }
        }
    ],
    "type": "ScheduleTrigger",
    "typeProperties": {
        "recurrence": {
            "frequency": "Hour",
            "interval": 1,
            "startTime": "2020-06-30T13:43:00.000Z",
            "timeZone": "UTC"
        }
    }
}

}

Thanks, Lukas