Good news to report. Heard back from support and they provided me with a BETA version of the firmware (1.0.0 Build 20170120 Rel. 22124(US)) that seems to have fixed the "unicast blocking" issue while...

Glad I am not the only one with this issue. I reported the same issue with the RE350 via an Amazon review a couple of months back. The TPlink extender blocks unicast packets for 5 minutes when in AP...