calculator in iphone gives wrong answer sometimes.

I have been using iPhone for years and After iOS 11 I have been difficulty in calculations as calculator is very unresponsive, like if you perform 1+2+3 fast or even in normal speed you won’t get 6. In calculations when I touch operators I need to wait a sec for its response to glow. I think delay time is more.

No one has enough time to wait for operators. I hope this issue will be resolved soon or I will be guided.

Thankyou