I had the same problem I was guarding the ship they where fighting borg and I had to stay put when sudenly three hits destroyed my ship out off nowhere.
No one can explain this but all STF's realy need an upgrade.....
Its the engine of the game, it has trouble when alot of effects are going off and some effects dont show which is why u get hit sometimes by nothing.
They need to update the engine a bit as todays gfx cards can handle alot more than the engine can do.
Well it's doing it frequently again and with Cryptic making Borg hit harder it's not fair for us because how can we defend against something we cannot see.