[highenergystar]

Could this be from the test of the nuclear powered hypersonic missile that Russia is developing [0]? Those things aren't designed to 'land' no pun intended

[0] https://en.m.wikipedia.org/wiki/9M730_Burevestnik

[catalogia]

My first guess is their nuclear powered torpedo, 'Poseidon', aka STATUS-6, or Kanyon:

https://en.wikipedia.org/wiki/Status-6_Oceanic_Multipurpose_...

I'd sooner expect it in the Arctic Ocean, but who knows.

Edit: Some supporting evidence from twitter: https://twitter.com/FrankBottema/status/1276930424170844162