Main monitor sometimes goes to sleep after boot

Hello,

I have an issue in Mojave that started not long ago. If I recall correctly, it might have been after I switch to WhateverGreen kexts.

The issue is that sometimes (there isn't a pattern, really) after boot, my main monitor (Dell U2415, connected via mini DisplayPort) goes to sleep. Sometimes (more rarely), even my secondary screen (Dell 2408WFP, connected via DVI) goes to sleep as well.

To fix this, I usually either turn off the monitor completely and turn it back on after a few seconds, or (when my other monitor is working) I go to System Preferences -> Displays and click on "Detect Displays" (by holding the Alt/Option key while the window is open).

I tried to re-install the OS again with updated kexts, but it didn't solve the problem.

SMBIOS: iMac 14,2

MacOS version: Mojave, 10.14.2

CPU: Intel i7 4790K, "Devil's Canyon"

Motherboard: GA-Z97X-Gaming 3

Memory: 32GB (4x8GB) G.Skill Ripjaws DDR3 1333MHz (F3-1600C9-8GXM)

Any ideas? Any help would be highly appreciated.

Thank you!