Using a brand new display port cable from the same new package I got the monitor from.
Used at least 6 different 17.x.x drivers for the Asus Strix RX 470 4GB always using DisplayDriverUninstaller and safemode before installing any driver.
When the computer starts, the screen is ALWAYS 144hz and doesn't show the 240hz as an option when you boot the computer: https://puu.sh/ueBDn/b9d4089879.jpg
Also when I start the computer my other screen won't detect input, powering off the BenQ XL2540 and putting it back on from the monitors power button. My second monitor gets signal after it and lights up the screen with windows background. It also changes the XL2540 to 240hz: http://puu.sh/ueGEx/a12a510457.png
The Monitor Link Failure message comes to radeon notifications when you've done the 240hz powering off/on bug and launch Counter-strike: Global offensive with 17.x.x drivers. It says no signal for a moment and then it downscales the hz and starts to show the CSGO menu screen. Going to the AMD Radeon settings "NOTIFICATIONS" after launching CSGO it says:
Error The system has detected a link failure and cannot set the requested resolution and refresh rate. Your display might not support the requested resolution or there may be an issue with the cable connecting the display to your computer.
i5-4690k 4.2ghz, Corsair 8GB DDR3 1866mhz, Asus Strix 470 4GB, Asus Z97-Pro Gamer, XFX XTR 550W 80+ GOLD full modular, Samsung 850 EVO 250gb.
Windows 10 64-bit build 14393
Here is another good example with more people using 17.x.x drivers having 240hz monitor link failure problem:
Message was edited by: Jaykay, 30/3/2017 update made it even more clear and fixed title.