So, looks like you are using DevAppId (480), a lot of other devs are using it. So probably you are searching for their session and you are not able to connect to them.
There are few solutions for this case:
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Increase number of Max results in Find Session
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If you have steamworks, buy a place for new application - then you will get your unique app id.
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Highjack app id of one of the game from you steam library that you and your friend own and that doesn’t offer multiplayer support.