Connecting external monitor sometimes requires Mint to be forcibly powered off

[rmwiseman]

I recently upgraded to LM 18.2.

I experienced a problem connecting a projector via VGA yesterday. I was trying to sort out the resolution and one thing I tried was "mirror displays" but that wasn't what I wanted so I clicked the revert button. The screens both became confused, with the whole screen (including the reversion dialogue) displayed multiple times (tiled) but it never finished reverting. The mouse pointer was still there and movable, but nothing on screen could be interacted with and nothing I tried on the keyboard (e.g. restart Cinnamon, force log-out, open the Start menu) had any effect. I had to power down the machine forcibly.

This morning I succeeded in replicating the issue using a VGA-connected monitor. The result was the same. I thought I would video the process on my phone to post here, but when I reconnected the "offending" monitor it froze the display in a similar way to when the original issue occurred and again I had to forcibly power of my machine.

Is there somewhere I can look to see what went wrong?

Is there a way I can reset my external monitors?

I'm currently connected to another monitor via mini display port and that's fine - although I daren't make any changes to the settings!

The process that originally broke things was:

1. Connect monitor via VGA.
2. Open display settings.
3. Drag the monitor to above the laptop's monitor and Apply.
4. Tick "Mirror displays" and Apply
5. Click the Revert button
6. Screen doesn't revert properly and becomes unresponsive except for the mouse pointer being movable.

This was what I did the second time too (with the monitor instead of the projector) and the result was the same.

[bpeters07]

I just upgraded from 17.3 to 18.3 a couple of weeks ago. I've had the exact issues you've described (tiled display, movable mouse, nothing clickable, etc.) with when plugging in both VGA and miniDP cables to external monitors. Like you, I had to hard-restart my laptop. Each time, when I plugged the external monitor cable in again, it was fine -- I haven't been able to reproduce the issue.

My only comment about displays is that I manually changed my display to 1600 x 900 (the default setting on Mint made everything a bit too small on my laptop's screen, at least for my case). It seems, however, that when plugging in the cable, the laptop screen was attempting to display at the originally, higher resolution default. Maybe it's something with the switch?

Just posting to see whether you've managed to resolve it or discover more about what's causing it.