I think you've posted in the wrong forum, unless your a beta tester for SHO, than I envy you.
But to help your problems, remember to submerge and travel at a slow speed, preferably Ahead Slow. This will allow you to "hear" your enemy better because your engines aren't overpowering the sound area.
Also, the longer it has been since the contact update, the more faded it will be. So depending on what kind of ship was traveling, it could be hundreds of miles away by the time the contact fades out of your map.
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