[DESKTOP] One monitor does not work properly after startup

[Spectrum]

Hi! I have this problem: I have two monitors (an Acer and a Samsung). My graphics card is a GeForce GTX 1060. Until recently both monitors worked fine in Kubuntu. Recently I have this problem: The Samsung monitor looks fine when the BIOS and Grub are running, but when Kubuntu starts it goes black. I can see that Kubuntu still COUNTS it as connected - e.g., I can move windows to it and back using keyboard shortcuts. But nothing shows up on it.

Workaround is:

1. Go to System Settings -> Display and Monitor.
2. Disable the Samsung monitor and apply.
3. Re-enable it and apply.
4. Now it works as usual - until the next reboot.

It started happening yesterday. I do not know that I did or changed anything to trigger it. I tried to update all my software using Muon, but that made no difference.

Does anyone have an idea for how to resolve this?

[Spectrum]

UPDATE: Alternative workaround found:

1. Press PrtScn to launch Spectacle.
2. In Spectacle, click "Take a new screenshot".
3. Suddenly the other monitor wakes up!

[Spectrum]

UPDATE: Alternative workaround found:

1. Press PrtScn to launch Spectacle.
2. In Spectacle, click "Take a new screenshot".
3. Suddenly the other monitor wakes up!

Updated finding: Taking a screenshot with scrot or KSnapshot does not wake up the dark monitor. But in both cases the screen shows up correctly on the screenshot (i.e., not dark).