My iPhone X had been experiencing lag which I simply could not explain for the past few weeks other than assuming that iOS 11 was poorly optimized since the A11 Bionic chip should be a beast. After dealing with “Congratulations Amazon user” popups intermittently on almost every site I visited, I decided to clear my Safari data and my iPhone X immediately went from inexplicably lagging every few seconds to becoming a silky smooth experience. Performance is night and day. In my decade of iPhone ownership, I’ve never experienced anything like this. Somehow, what I’d have to assume to be malware had infiltrated my Safari cookies and was affecting my system performance. I’m on 11.2.5, the latest iOS version. Thankfully this is as simple as clearing Safari data, but I’m surprised to see this on my iPhone. Apple has superb security and I’m sure it’s an anomaly, just a heads-up.