I've had at least 3 just this week alone:
1) Spotted by a plane BUT did not get a spotted indication on my screen. I was sunk sailing into torps. I asked how a full torp salvo hit me and enemy ship replied that I was spotted the whole time.
2) Spotted by a BB from 6km in Kamikaze (detection 5.4km with CE) as I approached for torps. Had not fired guns. I was sunk. (I think the game did not account for my CE captain because stock Kamikaze detection is 6km.)
3) Enemy BB was showing (and stayed) solid red (not outline) and ship was not moving on mini-map or screen while behind an island for about 2 minutes BUT then pops up beside me at 2.5km in open water. I was sunk. Enemy replied he was wondering why I had not torp'd him, which is what I'd positioned to do. I had torp aiming indicator pointed at ship but indicator never moved.