cursor jumps around on iphone while typing, it happens on my 6s and my sister’s iphone too. i gave the latest ios update and rebooted it.

I have an iPhone 6s, updated to latest iOS version, rebooted. When I answer an email, the cursor jumps to different places randomly. Even now, the cursor is above the typing line. It’s also happening to my sister’s iPhone 6. Any suggestions, Apple friends?