[FS#863] ath9k failure with AP+11s VIFs ("unsupported hw bitrate detected")

[LEDE Bugs]

The following task has a new comment added:

FS#863 - ath9k failure with AP+11s VIFs ("unsupported hw bitrate detected")
User who did this - FreifunkUFO (FreifunkUFO)

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its also happening with ath9k on AP+11s VIFs (f.i. on freifunk meshes)
i think its THE well-known problem of the last months, mostly called "wifi will break until a wifi scan is started".

2 weeks ago i saw that problem on a 5ghz (!) device (ubnt-loco5m)
[135091.754940] ath: phy0: unsupported hw bitrate detected 0x1b using 1 Mbit

there were many thoughts about it. sometimes it seemed to be broken/mad wifi-client-devices (at one location the mistake was only on weekends) or when people were using many windows mobile phones.
other ideas blaming ANI (please try to disable and enable ANI) or HCS. Or pathing ath9k (0xdeadbeef).

meanwhile many mesh-communities (like freifunk, libremesh..) have very many bad or very bad workarounds about that. (so even neoraiders wifi will recover after an hour)

see comments/links on https://plan.leipzig.freifunk.net/issues/252
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=863#comment3616