As far as I understood, sneaking currently displays a kind of effect that might be used for "Hiding in Shadows" some day (and then gets removed from sneaking again), just as "proof of concept", or technical test.
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Oh, Boeven might be right: It is not about the movement of the character in the game world, it is about executing the client and launcher at all.
Therefore the correct placement of this thread in "Technical Help: Problems BEFORE entering the game".
My recommendation: Find an experienced computer user who is able to chat with our developers in IRC to find the reason via "live support"; a forum is not the best place, because facts have to be requested and answered again and again and again...