HP ProDesk 600 G2, two monitors - blank screen for up to a few minutes

Good day,
 
We use various devices of this series. Currently, sporadic intermittents are increasingly associated with the connection of two monitors. In the course of a working day there are about 2-3 dropouts. The monitor remains black for up to 5 minutes, the second monitor usually works during this time. We have already tested various monitors, mainly AOC or Benq. The monitors are connected via Displayport, we also tested VGA. The BIOS version is up to date, as well as the drivers.