Have you tried deleting the wifi connection and then re-entering and re-establishing the connection? We have the Amber update, and have not had an issue with wifi disconnecting - it seems to work just as it did before, which is to say, it works.
Let's stabilize your WiFi connection! Have you tried what SuzyQ suggested? What is the current software version number http://vz.to/19It7MD of your Nokia Lumia 928? Keep me posted so I can further assist. Thanks!
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