On reference stardate 2/1912 the Genser and five other vessels were escorting a convoy of neutronic fuel carriers to the rimward frontier when the ship's sensors detected a small object traveling on a parallel course to the convoy.
Communications couldn't be established with the object so the Genser broke off from the convoy and headed off to investigate the object. As the Genser approached the object it disappeared and then reappeared shortly after. When the rest of the convoy couldn't establish contact with the Genser they investigated and found that the object had disappeared along with the Genser's crew.
The Genser continued on active duty but the whereabouts of her missing crew or the mysterious object was never determined. (FASA RPG modules: Federation Ship Recognition Manual, Star Trek IV Sourcebook Update)