http://wccftech.com/ios-11-2-beta-fixes-a-weird-calculator-bug-that-prevented-it-to-perform-a-simple-calculation/

Apple has called iOS as the world’s most advanced operating system in the world multiple times in the past. However, its recent release of iOS 11 begs to differ because it is crawling with a bevy of bugs. Similarly, a bug in iOS 11 calculator app was discovered recently, that prevented users to perform a calculation as simple as 1+2+3. While the answer to the aforementioned calculation should be 6, chances are pretty high that you will either end up with getting 23 or 24 if you type it rapidly. However, in the latest iOS 11.2 beta, Apple seems to have fixed the issue.

In all versions of iOS 11 before the release of iOS 11.2 beta, a calculator animation causes symbols to be ignored or skipped when entered quickly. The issue basically occurred when a user tried to add 1, 2 and 3 rapidly. At this point, the second tap on the ‘+’ symbol is not registered by the operating system for an unknown reason. In addition to this, the issue seems to not exist when an individual tried to tap in the digits slowly or takes time between each tap. Since the issue was on iOS 11, it was, hence, present on all iPhone and iPad models.