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Hello @Ianmac123, have a warm welcome to the Fitbit Community, it's great to have you on board. 
When you updated the OS on your phone, were you asked to log in to your account once again? When was the last time you synced your tracker before the OS update? In this case I would like to suggest you to go to your online Dashboard and check if the information is showing there. If it is, it's possible the app is not displaying the information correctly, which is why I would like to suggest the following:
- Force-close the Fitbit app by double tapping the home button on your phone and swiping up the app.
- Log out from your account, then log back in. (this is a manual log out instead of an automatic one prompted by the app itself)
I hope this can be helpful, give it a try and keep me posted in case you need anything else. 
Best Answer