Lost all my data

First, have you activated Dropbox or iCloud synchronization in oneSafe?
If this is the case, could you please check that the "switch" is still turned on in:
- oneSafe iOS > More > Synchronization
- oneSafe Mac > oneSafe > Preferences > Synchronization?
If not, please turn it back on. If nothing happens, please refer to 2) below.

The other options:

1) Have you done oneSafe backups in the past? If this is the case, you could import the most recent backup in a new fresh install of oneSafe.
* Make/Restore a backup, go to More > Export a backup

2) In oneSafe, if you have the synchronization turned on, and there are missing items (or no items), rebuilding the oneSafe local cache could fix the issue: go to oneSafe > More > Synchronization > "i" icon > Rebuild Cache

3) Have you activated the automatic backup of your iOS device in iTunes or in iCloud (when configuring iOS the first time) including App’s data (not done by default)? If this is the case, you can restore your device with the most recent backup of your device, including oneSafe's items.
http://support.apple.com/kb/ht1766