MacOS Sierra not recognizing external displays and going black

I have the same problem.

This is the message I get on the Console app when attaching an external display (Dell ST2420L) via a Thunderbolt to HDMI cable (it's for the WindowServer process):

[ERROR] - Driver reported mode info is out of sync with current mode info. Display 4280500, driver's bytePerRow = 10240, driver's width = 3360, stored width = 3360. Forcing rowbytes to be 4*modeInfo->ioModeInfo.nominalwitdh.

The message is repeated several times, and also appears when de-attaching the cable.

I have the same issue as well. When attempting to connect with an external projector as a second monitor, the projector does not connect properly and all I see a blue/default screen. Another issue I noticed is that when I start my computer with the projector connected to the iMac both screen go blank/purpleish black and all I see is a cursor that can be moved around. However, when I unplug the thunderbolt adapter to the projector, the iMac screen comes back to the login screen.

There is definitely something wrong with macOS Sierra and I would really like to go back to the previous version.

I have the same console message as @oleguerilustrum, and I have recently updated to Sierra, but I have *never* attached this macbook to an external display. So I'm not sure what the reason for this message is, but it's nothing to do with external displays.

Same for me.

And external monitor is not working since upgrading to Sierra.

I have the same issue as well. When attempting to connect a second monitor with a DisplayPort to VGA adapter, the monitor does not connect properly and I see is bluisht screen. I've tried to reset NVRAM.

I don't see any kernel panics as far as I can see.
Did you try downgrading to El Capitan already?

I forgot to mention in my previous post that this issue happens ONLY when connecting with the Thunderbolt port to the external display with a Thunderbolt to HDMI cable adapter.

When I connect it with the Macbook Pro's HDMI port (with a regular HDMI to HDMI cable to the Dell external display) then it works. The only issue then is that several times a day, the external display goes black for some seconds (says Entering sleep mode) and then goes back to normal. This last issue already happened to me with El Capitan, and using an HDMI-to-DVI cable or using another different external display doesn't solve it (which makes me think there is an issue with the Mac's HDMI port).

My system is a MacBook Pro (Retina, 13-inch, Late 2012) with an Intel HD Graphics 4000 1536 MB graphics card.

Same problem

after upgrade external monitor does not work anymore

[ERROR] - Driver reported mode info is out of sync with current mode info. Display 42737c0, driver's bytePerRow = 6144, driver's width = 1680, stored width = 1680. Forcing rowbytes to be 4*modeInfo->ioModeInfo.nominalwitdh.

Control keys on bluetooth headphones does not work anymore too

Bluetooth Controls not working in Sierra

sierra is the biggest peace of **** I ever install to my mac's !

looking a way to downgrade this

They released an update today (October 25th 2016) that fixed this issue for me. Connecting my MacBook Air to an external display works again!

Hmm... no any updates for me today

I have the same issue. I just got a new external monitor (HP Pavilion 27xw) and tried connecting it to my Macbook Pro (Retina, 13-inch, Mid 2014). When I connect the monitor to my laptop via the HDMI cord, my Macbook's screen flickers once or twice, but then nothing else happens (i.e., the monitor does not show anything -- it goes into sleep mode as if nothing is connected). Upon disconnecting the HDMI cable, the Macbook screen flickers again. I get this console error when the monitor HDMI cord is plugged in or taken out:

"[ERROR] - Driver reported mode info is out of sync with current mode info. Display 4280600, driver's bytePerRow = 10240, driver's width = 3360, stored width = 3360. Forcing rowbytes to be 4*modeInfo->ioModeInfo.nominalwitdh."

I tried the connection first with OS Mavericks (10.9.5) that I had on my Macbook. I tried updating to a newer OS thinking it might help, so I just upgraded to Sierra (with the latest update from Oct 27) but still have the same problem -- the monitor still not recognized and I get the same console error.

I have tried all the suggestions listed here without success: Get help with video issues on external displays connected to your Mac - Apple Support

I also tested the connection by plugging in the monitor with the same HDMI cable to a friend's Macbook -- it was detected immediately and the monitor showed his screen (so the problem is not with the monitor or the HDMI cable).

I would appreciate any help from Apple.

Hi All

I have almost the same problem after update to MacOS Sierra.

I have Kernel Panic boot loop if my Macbook Pro connected to external 4k monitor using mini Thunderbolt display port. It worked fine with El Capitan.

I have done PRAM and SMC reset and updated OS Sierra to the latest 10.12.1. Still have the same problem.

Problem occurs only when I restart and power up my macbook with external monitor connected to it. Without connecting the external monitor, It booted up fine. Also, It displays fine when I connect mini display port after the mac booted up.

Anyone has any idea?

Thanks

Macbook Pro 15 (Mid 2014 with NVIDIA GeForce GT 750M) connect to Samsung 4k (U28D590) Display visa mini/thunderbolt display port.