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Gecko/20100101 Firefox/55.0
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If I install the NVidia drivers, from the repositories, and reboot with 2
Monitors activated, (4K and Full-HD), the log in screen freezes after about 3
seconds every time. If I start the system with just one monitor connected (it
does not matter which), I can log in without problems. There is also no
problem, when I turn the 4K monitor off before I see the log in screen, log in
just with the Full-HD Monitor detected, and then turn the 4K monitor on again.

I think it has to do with the detection of the 4K monitor, because the log in
screen freezes every time the 4K monitor is detected by the system. That's why
it seems to be a driver problem, it does not happen if I install the
open-source driver or the "original" drivers from the Nvidia website.

With KDE 5.10.5 installed, directly after new system installation

Reproducible: Always

Steps to Reproduce:
1. install Nvidia driver from repository
2. install them
3. reboot with 2 Monitors, one has to be 4K
4. have a look at the log-in screen
Actual Results:  
The log-in screen freezes after about 3 seconds, I'm not able to log-in in the
graphical environment anymore.

Expected Results:  
detect the 4K monitor correctly and give the chance to log in to the system
(can still use terminal with CTRL+ALT+F1, F2...)

I wasn't able to find any logs with relevant information, sorry. :(

I have an Intel Core I7-6700K, Geforce GTX 1800 and a 4K monitor.