RE: OptiPlex 3040 micro, dual monitors using HDMI and DP ports, DP connection unreliable
This does not sound like a hardware failure. Did you check/test all of the Windows 10 power management options? Specifically the PCI Express- Link State Power Management setting? Or just set the Windows 10 power management to High performance and retest. Also, if the U2415s USB upstream cables are connected to the computer, be sure to disable the USB selective suspend setting.
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Run the PC pre-Windows diagnostics
Where do I find my Dell PC Service Tag or Express service code?
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