GWX has the same bug - I called it "ghost ship".
You can find ship, sink her and get ... no renown.
You can see how she is sinking but no info "she's going down".
I thought it depends on shallow water but please see few screenshots :
Large cargo on horizont (water deep more than 1000 m)
deck gun fire
she sunk and ship disappeared from main map
I repeated attack by torpedos and the same result.
I'm very disappointed with such bug. Can anybody tell me what to do ?<div class="ev_tpc_signature">