Portrait mode lag & freeze
 

To start, everything works fine when I have two displays connected and they are both oriented as landscape.

The problem arises when you set either of the two external displays in portrait orientation, either left or right, regardless of which external monitor you set it to. What happens is the screen will not refresh the image unless the cursor is on that display, and even then it is laggy.

The second your cursor leaves that display the image on that display freezes and will not update or refresh until the cursor has returned to that display.

Another thing to note is that 90% of the time, when the cursor leaves a display that is set as portrait, the image of the cursor is still seen on the display when in reality that is not where the cursor really is.

I have attached the logs from the dubug tool as well as some videos showcasing the issue.

I have similar problem on computer with nvidia card. Landscape works without any problem but in portrait mode screen is refreshed only when mouse cursor is moving on that display. When I make screenshot it shows newest state, so the memory buffer is refreshed but it isn't visible on the display.

I don't have any problem on second computer with intel+ati - portrait mode works without freezing.

Edit:
I've installed Ubuntu 20.04 and checked what works on fresh system. Problem with freezing in portrait mode exists only on nvidia proprietary driver. On nouveau it works without freezing. So the problem is probably connected with nvidia proprietary driver. The problem isn't new. I saw a message posted almost 3 years ago with exactly the same problem described.

Workaround:
1. Switch to the nouveau driver if you need portrait mode.
2. Rotate your monitor to landscape if you need performance provided with proprietary driver.