Why does the monitor not turn on after idle / when turning on the PC?

Question

Monitors

Good afternoon!

I have run out of ideas, some kind of devil is happening, help me figure it out: two monitors are connected to a computer with an nvidia quatro p1000 video card. Monitor A works without problems, monitor B does not show a picture when:
1. you turn on the computer
2. after about an hour of inactivity (the employee leaves for lunch, blocks the computer, the monitors go out)
You log in to the OS, one monitor works as it should, the second has a black screen , but the mouse from the monitor A goes there! and does not stop at its edge. It is always treated in one way: turn off the power of the monitor with the button and turn it on - the picture immediately appears.
What was done:
1. updated all firewood and bios with the dell command update program (dell computer) - did not help
2. installed the latest nvidia quatro drivers (clean install) - did not help
3. connected to another video card connector (swapped) - did not help
4. changed DVI wires - mini DP / DP - mini DP - did not help
5. reset monitor settings
6 I changed the monitor to a replacement one - it helped, the flight was normal for three days
You might think that the problem is in the monitor, but I tested it on another computer and everything is ok. 10-15 times I waited for an hour and a half and woke up the computer, it works like a clock (DP connector).
the replacement monitor did not work in any video card connector, but in the second one it worked for three days, and with the same cable in the same connector, monitor B is constantly buggy.
Right now the monitor returned back to the user - the problem remained. Strongly does not interfere with his work, so I want to try to find the reason. Can you tell me what else to check?

ps: in the device manager with such a glitch, both monitors are visible. if you connect remotely during a failure, both monitors are visible, the picture is as it should be, everything is configured as needed in the screen parameters

Answer 1

= I tested it on another computer and everything is OK =
Were the testing conditions the same as the original ones? For example, ambient temperature? Is it not that the client has a cold office at work, and your test room is very heated?