Mac OS Sierra: Erratic resolution of Dell 4K P2715Q monitor

I also find it disappointing when it worked before.

Interestingly I have noted that if I run the two Dell screens alone or with the native display on in a screen saver (I use the Apple TV video screen saver) mode then the issue never occurs, the screens just keep playing the saver.

The black screen/blanking seems restricted to undertaking activity in the desktop, like say using MS Office, surfing the web, writing emails or something similar. I also think it is reduced in frequency by having all 3 screens (2 x Dell 4K at scaled resolutions) AND the rMBP screen in retina mode (all at 60Hz) operating at the same time. It still happens just less often. Admittedly I haven't quantified it yet. Although I am recording time points of occurrences with a view to trying to spot a common entry in the console logs to see if I can establish what is happening. No luck yet.

Hi

A minor update for you. I have been running reasonably OK after the most recent SMC and NVRAM resets. Then it started again.

This time I have been paying more attention to what I am doing and I think I can run for a long time without issue just surfing, watching videos, writing emails, etc.

However, when I use Microsoft Excel with complex worksheets or simple worksheets, with a single file open or many files open or just having the app open I seem to get the issue occurring. Its unpredictable but Excel seems to kick it off, I am not sure about other office apps. I am using Office 2011.

I have no idea how these things relate but could it be that the older Office version has introduced stability issues when open?

I use 2011 as I didn't like 2016, although I could start using it if pushed.

Nevermind, delete this post!

Hi

Another update. MS Office 2011 Excel was a red herring, it also happened in Word and outside of Office suite too. I did see a CoreAnimation error dealing with Office in the console logs but nothing else.

I have erased and done a fresh install of Sierra and I am now using Office 2016. I have had several instances of the same problem with the an intermittently blanking display on the frontmost thunderbolt 2 port (one next to USB3.0 socket not the one next to the power socket). I can run on this port alone without issue.

It is really hard to see anything in the logs. I have reported this via Bug Reporter but I am unwilling to do a complete dump as requested by Apple as they warn me that they will be able to see personal iCloud and other sensitive information and so on. It literally is a complete dump of everything. I would need to run this device as a non-production machine with a vanilla iCloud account to be comfortable with giving over that level of data.

As I have said before this issue is coterminous with Sierra installation. It doesn't matter if it was an upgrade or clean install. So its either Sierra use of the GPU/drivers or I have developed a simultaneous hardware fault. I think the latter is unlikely but possible.

At present I am living with it but I am contemplating rolling back to El Capitan too just to absolutely prove its not hardware. Even though I have done that earlier.

Roll on 10.12.2!