Iphone GOS no longer reroutes
Too little information.
It's the app that reroutes. That app are you using? Waze seems to be the most used and it does reroute if it detects traffic issues.
Also, the app has to be giving directions to a destination for traffic reroute to work. If you're just driving around with the app open and not using navigation then the app doesn't know that you need to avoid traffic issues.
And last, with all the IOS updates lately, have you also updated all your apps?
Hope this helped.