Been chasing my tail for weeks and finally figured this one out.
Intel “AC-8260” comes factory default enabled with “HT Mode” set for “VHT Mode” which stands for “Very High Throughput”.
When this was enabled on my Cisco Aironet 1142 Wireless Access Point configured as an “Office Extend Access Point” (OEAP for short), I got very NO throughput. I mean, ZERO packet transmission and 100% packet loss. I chased my tail for weeks swapping hardware, making changes to VLANs, you name it. Finally I stumbled on this “HT Mode”.
I disabled “HT Mode” (Computer Management –> Device Manager –> Intel Dual Band Wireless AC-8260 Properties –> Advanced (tab) –> HT Mode –> Disabled (drop down menu)) and my connection problems with away. ALL OF THEM. Not a single packet dropped. Not a single hiccup on the OEAP. Voila! Clear as day.