BioWare confirmed today that the server was hit by an unexpected rollback that affected some of Harbinger’s population: “Before the server was brought down, we confirmed that some players did experience a rollback. Unfortunately, there is no way for us to restore the progress that was lost during that time period. We are looking into procedures to avoid this from happening in the future.”
On the forum thread, players reported several hours of progress lost. The studio apologized for the rollback.
Source: Official forums. Thanks to Khalith for the tip!