Sched. refresh for Dataflows failing at some hours but succeeding at other, reports updating slower

Since last week we started having issues with some of our Dataflows (Gen1) failing to refresh at certain times (7:00 AM or 9:00 AM CET), but they succeed to refresh at other scheduled times, such as 8:00 AM. Some reports now also take much longer to refresh than usual. These reports and dataflows have been scheduled and updating without issues since months
We dont have premium or Fabric capacity, only Pro licenses, so we dont manage any usage ourselves. Any idea what might be causing this and how to fix it?