Hi @StuFather! The monthly and yearly views use a different kind of Timeline Item object - “Simple Items”, which are simplified versions of the originals, to reduce memory use when displaying large amounts of data on the map.
Those SimpleItems get updated daily, when iOS runs Arc’s scheduled task for doing so. However often iOS won’t let the task run for long enough to finish the job, so they fall behind.
To get around this, Arc will run those updates when the app is in the foreground, plugged in to power, and you’re viewing a monthly or yearly timeline view. So plug the phone in, open Arc, then switch to monthly or yearly view and swipe through to the months with missing data, and Arc will start working on filling in the gaps.
It might take a few minutes to see results, depending on how behind it is.