In November 2017, Russia test fired the Burevestnik (SSC-X-9 Skyfall) nuclear-powered cruise missile from it's test location at Pankovo.
Distance for her from the shore and the possible test site is circa 7km~. One other vessel appears to be in the same vicinity at the time (next tweet)
Note the position of SEREBRYANKA is via sat. and isn't as "live" as some AIS feeds so it's hard to tell if she's still there as current data is 2+ hours out of date already.