Greetings, I am not sure where and how confirmed this hull-number "SF-156" come from.
I think from the latest Russian evaluation of the incident, the sunk Siebel was "SF-21": technically the only one sunk during the battle (and not scuttled). While SF-12, SF-13 and light ferry SF-26 all scuttled by Germans ("SF-26 was the craft later recovered by Soviets and placed in service as "DB-51").
Apparently, "SF-21" experienced leaks (i have never fully understood if it was due technical reason or possibly splinter damage fighting against the survived ground gun left on the island) and damaged by crew before leaving her.
Gunboat Nora found the floating Siebel and shelled her at point-blank, sinking her. Technically a wasteful sinking, because the trigger-happy commander could have simply seized her.