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    #1

    Third monitor works on login screen, but stopped working in desktop

    This is a strange one to me. I have a Macbook 2015 with Kubuntu 19.10 installed and all the latest updates. It's a pretty vanilla install. I have a second monitor through the thunderbolt-minidp port that has always worked.

    But, I have a third (cheap) monitor that I have tried through the HDMI and also through the second Thunderbolt to HDML cable. In *both* cases, the monitor has worked in the past, and I went several weeks with all three monitors configured and humming beautifully.

    Today, however, the third monitor started flashing intermittently and then went out. I have checked all chords and connections and they are fine.

    The weird thing is that the monitor works fine when booting and on the lockscreen. It's only once I enter the desktop that Kubuntu loses the third monitor. I've checked the Display Configuration Settings and the third monitor simply isn't showing. I have swapped the two external monitors and the same thing happens. It seems that my Plasma Desktop only accepts two monitors now, while the login screen accepts three.

    I am not sure which other logs to look at, or where to go from here. Does anyone have any suggestions?

    Much appreciated.
    Tags: display, monitors, plasma 5
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    #2
    Well, no major suggestions but a small piece of info: The reason the third monitor works on boot but not on the desktop is because the video driver isn't loaded by the boot manager. However, I do find it odd that it would work at screen-lock after logging into the desktop so maybe the screen locker doesn't use the viedo driver either.

    All this suggests the issue is somewhere in the driver or configuration. My first test would be to boot to a LiveUSB of some distro and see if the third monitor lights up there. If this all started only three weeks ago, it might be worth it to determine what has changed in that three weeks, liek what updates were installed, etc.

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      #3
      Well @oshunluvr, it appears you are right. To clear things up, it worked fine for several weeks and stopped working today. I *did* install some updates today. I rebooted in a live usb and three monitors worked by default.

      But, I installed a lot of updates today. Not sure how to find the right update to rollback. I've tried to rollback all my updates, but got a lot of `E: Version '5.65.0-0ubuntu1~ubuntu19.10~ppa1' for 'qml-module-org-kde-kwindowsystem' was not found` errors.

      I found https://unix.stackexchange.com/quest...ing-goes-wrong most helpful.

      Does anyone know a way to either 1.) Rollback these updates or 2.) discover which was the culprit?

      For posterity, here is what I tried to rollback too: https://pastebin.com/ghX95Vbz
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