Community Moderators ensure that conversations are friendly, factual, and on-topic. We're here to answer questions, escalate bugs, and make sure your voice is heard by the larger Fitbit team. Learn more
A warm welcome to our new friend @Eviel! Thanks for stopping by! 
I'd like to know if you have checked you have the "All-day sync" option enabled on your iOS device? To do this, please do the following:
1. Go to your iOS Fitbit Dashboard.
2. Tap the "Account" icon.
3. Tap the tab where it's your tracker's name.
4. There you'll see the "All-day sync" option, please make sure is enabled.
If it is and your tracker is still not syncing as it should I'd suggest you do the following:
1. Restart your tracker.
2. Double tap the home button on your iOS device. Your open apps will show on your device's screen.
3. Close the Fitbit app by swiping the app image in an upward motion.
4. Reopen the Fitbit app.
Hope this helps, let me know how it goes! 
Best Answer