I heard claims it was possibly a detonation in AK-130 130mm artillery shell storage. That sounds more in tune with what the official news are talking about.
Unfortunately we may only get the real view once someone actually deploy submersible there to inspect her wreckage.
May I ask, why it is so much unbelievable and more likely sunk by accident than indeed an Ukrainian missile attack?
Well if you ask me. It started from the weather map At the time of her being supposedly attacked there were storm, Sea state 6-7. Now Neptun shared considerable amount of characteristics with Uran including a 4 m terminal phase. This not really bodes well with sea state and Uran itself is rated for sea state 5-6. The missile will indeed fly higher in mid-course phase to acquire target. This presented the opportunity for early detection, except it might be not long. Before the missile dive after the acquisition phase is complete.
But flying at sea state 6-7 at 4 m can actually risk the missile hit wave and at speed of 500-900 km it might be like hitting a wall. That's what i am thinking of.
While mines, there are reports that mines around Odessa got washed away and even there were reports that mine were actually found near Bosporus. The thing is How many of them still not found and freely floats around. That one still floating can be the joker that brought Moskva her sad fate. Russian themselves had bit of safety issues which lend me to also think of the accident theory.
I understand tho that my thoughts above is not perfect e.g Missile can use its own radar seeker for wave avoidance or simply be set to fly higher (e.g 5-7 m) during terminal phase. and