Monitor stays in sleep when daisy chained via DisplayPort

tl;dr

Run the followind command on startup, and the problem will be virtually hacked solved:

xset dpms force off

Cause of the problem

After some search I found this forum post and it turned out that everything works properly except that the monitor is stuck in sleep mode. If you wait for the system to sleep (or force it) when it wakes, everything will go back to normal.

According to the user replies, it seems like that this problem is common when you use Dell monitors with an nVidia graphics card.

Solution

As fabbari pointed out, you can force the monitors to sleep with the command xset dpms force off, so you just need to move the mouse and everything is back to normal. This is still more of a workaround, but if you search for "startup" in the dash and add a new startup application, you can paste the command so it will automatically run on startup. This happens so seamlessly, that you doesn't even notice it, so I consider it a perfect solution.