I have 2 or 3 out of probably 15-20 WIFI client devices that have problems with my LEDE/OpenWRT routers. The devices with issues are a Roku TV and 2 different Amazon Fire TV sticks (2014 and 2016 generations).
iOS devices, windows laptops, etc. are fine. A Google Chromecast in the same location is also fine. The devices connect but then disconnect and/or have really poor throughput, pings wind up with multi-second RTTs with packet loss.
I've tried two different router/APs, a TP-Link TL-WDR4300 4300 hw 1.3 and a RouterStation Pro with an ATH5K card. I've tested LEDE Reboot 17.0.1, Chas Calmer 15.05.1, and Barrier Breaker 14.07.
If I swap in an Asus TM-AC1900 (a rebranded RT-AC68U) running the stock firmware (3.0.0.4.376_3181) everything is fine.
I unfortunately don't have good notes, but I seem to recall things got worse somewhere around the Barrier Breaker -> Chaos Calmer releases.
I'm sorry this is fairly vague, but I don't know how to go about diagnosing this so that I could begin to formulate a meaningful bug report or correlate this to any existing bug reports. I've turned up hostapd logging. Sometimes i see 'disconnected due to excessive missing ACKs' and 'EAPOL-Key timeout', but I don't see enough of those to explain all of the problems. I'm guessing these would also be seen if there was just a very marginal RF connection. The signal levels don't look that bad from LuCI, though the data rates look very low.
I can share logs, provide more hardware details, etc. but I need some guidance on how to proceed in diagnosing this.
Thanks for your help.