On boot, iMac Apple logo blinks red after update to Mac OS Sierra

Headhunter... i support you! I said it (and you said it) a million times on this thread but nobody listens. It is a software issue and apple support told me they were aware and will be fixing it in a future software update. Not everyone in apple support is aware of every single bug. So some people in support may say "I never heard of it before" but you can rest assure that the developers are fully aware of this problem.

As I said before..:: it is a software issue. It doesn't effect anything else on the computer. Don't waste your time going to the Apple Store. Stop wasting your time complaining. Just sit back and relax with a drink in your hand. Lower your blood pressure. The fix will come in time.

Sorry, I have invested a lot of money into Apple (about $7000 in 3 years on 2 seperate iMacs) and a lot of lost time through emails, txt messages, phone conversations with Senior Advisors, Regular phone Tech Support, Apple Customer Relations, in store Applecare appointments, and now I have this iMac failing on me in under a year (regardless of where this issue currently stands - hardware or software). This said, I can only expect your response to be what it is, as you would have had to experience all I've been through to truly understand where I'm coming from, which obviously I don't expect you to (not being sarcastic). Anyways, I won't be commenting further on here, as I've contacted Apple with this issue and will hopefully receive a more diffinitive answer within a few days, oppose to many different comments I'm reading on here of what was said. I've never done the form thing before and thought it would help, but when your reading all different comments of what people are saying without hearing it for yourself, these forms become more like broken telephone then anything else.

I have the same problem as below https://discussions.apple.com/thread/7755119 We have both the same iMac model

Please download and install EtreCheck from http://etrecheck.com/

Run it and post the report here.

I have this same problem as well as at shut down I am missing the spinning progress wheel. Do you have that as well? I have a late IMAC 4k, 2015.

I have same problem to. Sometimes when i start up the computer some graphic card glitch problem appear too.

That happens to me too. iMac 21,5" 4K. Additionally, there are some lags in animations in programs such as iTunes.

same issue with iMac (Retina 4K, 21.5 pouces, end 2015)

Same issue here too. Sierra, Retina 4K 21.5inch late 2015

Apparently just a Sierra anomaly, according to several people who have asked Apple - to be fixed in an update. I have it too and it doesn't seems affect anything.

Not actually a 'problem' as far as I can tell. Apparently just a Sierra anomaly, according to several people who have asked Apple - to be fixed in an update. I have it too and it doesn't seems affect anything.

I have also had this red flash square on start up since installing Sierra. No fix has worked thus far.

Etrecheck is irrelevant to this issue and no help whatsoever. Stop trying to promote your software here.

By the way, my mother has an imac from 2012. She upgraded to Sierra and doesn't have the red box issue. This may be an issues with 2015 retina models.