USB 3 device poor connection in USB 2 host

[NiHaoMike]

USB 3 is supposed to be backwards compatible with USB 2, but I found that the USB 2 ports on the Raspberry Pi 3 will not make a reliable connection to some USB 3 devices like the D-link DWA-182 802.11ac adapter. I found that pulling the plug slightly out improved the connection, so it looks like the root cause is the USB 2 socket pins are making contact right on the edge of the USB 2 pins in the USB 3 plug.

Is that due to the socket being out of spec, the plug being out of spec, both, or an oversight in the specifications?

[NiHaoMike]

The Pi in question has been modified specifically to fix the USB power issue - bypass the current limiter, add some capacitance right at the ports, and supply power with a good PSU. With the mod, even 2.5" hard drives work.
I know for sure it's a connection issue since I can make it stop working by applying pressure at certain angles. Anyways, the workaround I'm using now is a short USB extension that is able to make a good connection.

[Halcyon]

I've had the same issue on some HP Z-series workstations. Not much that can be done apart from perhaps using a decent USB hub. This is also the reason why I keep a cache of USB 2 and 3 flash drives and storage devices on-hand.