It’s difficult to tell exactly what happened because I don’t know the specific steps and and other details. Normally an item gets removed from a device by sync only in two cases:
- It was removed on another device
- Pull and push operations can lead to loss of data (by design) if not considered carefully
Other that that, there are no known bugs that could lead to loss of data, and the syncing code hasn’t been touched in a while, so it’s pretty well tested.
However, the cases 1,2 are possible when setting up sync. For example, the tutorial items which are created when the app first starts have the same IDs on all devices. So if you rename a tutorial project or notebook and continue using it, there is risk of it being deleted after you remove tutorial items on another device.