You may have a hardware issue per this article:
Having the same issue. I don’t think the reply posted is related either, as that seems to be iTunes related. My partners phone flashes either “update error1” or “update error6” in the same way as your screenshot, just randomly when we are out and about. Current overseas so wondering if it’s carrier/ international roaming related?
After hitting back or cancel it seems to go away for a while.
Maybe it's some kind of advertisement in the game? You can also restore:
I'm currently travelling in China. I have been getting this message (and the update error6) message intermittently on my iphone. Yesterday when travelling back from a day trip near Shanghai I received this message several times while the car was on a highway. Interestingly, my wife's phone (an android) also put similar messages up at almost the same time. I did not have any games or apps running and have very few apps installed on my phone. Given the similar response of my wife's phone, this might be something to do with moving through different mobile coverage areas while roaming. It is still quite disconcerting..
I am in Germany and get the same error for both Error1 and Error6. I am using an iPhone 8+ and my wife has an iPhone 7. Both are doing it. Neither iPads show the error and one has a local sim card in it. It may be linked only to roaming using an Australian SIM. I have just turned 'Enable 4G' off and will see if that stops the issue. It has no impact on the operations of the phone in anyway. It clears for no specific time, then shows again.
Question: Update error1