No Wi-Fi connectivity after waking up from sleep on MacBook
Had very similar problem.  After wake up Wi-Fi icon shows "connected" status, but network does not work, i.e. even ping to my router does not work.  The connectivity usually resumes on its own after some time (dozens of seconds to couple of minutes), or after I do manual DHCP renew or turn Wi-Fi off and then back on.

The problem gone after I disabled DoS attack protection on my router.  It seems that my router treated Apple's rapid DHCP (https://cafbit.com/entry/rapid_dhcp_or_how_do) as DoS attack attempt.