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I started with a fresh installation of Raspberry Pi OS Lite (Release date: May 7th 2021, Kernel version: 5.10) and checked wifi state with iw reg get iw list.

global
country DE: DFS-ETSI
 (2400 - 2483 @ 40), (N/A, 20), (N/A)
 (5150 - 5250 @ 80), (N/A, 20), (N/A), NO-OUTDOOR, AUTO-BW
 (5250 - 5350 @ 80), (N/A, 20), (0 ms), NO-OUTDOOR, DFS, AUTO-BW
 (5470 - 5725 @ 160), (N/A, 26), (0 ms), DFS
 (5725 - 5875 @ 80), (N/A, 13), (N/A)
 (57000 - 66000 @ 2160), (N/A, 40), (N/A)

And then started the update to the latest version with sudo apt update && sudo apt upgrade -y.

After that update the wifi frequencies 5260-5700 were disabled.

Freq. Channel after before
5170 MHz 34 disabled disabled
5180 MHz 36 20.0 dBm 20.0 dBm
5190 MHz 38 disabled disabled
5200 MHz 40 20.0 dBm 20.0 dBm
5210 MHz 42 disabled disabled
5220 MHz 44 20.0 dBm 20.0 dBm
5230 MHz 46 disabled disabled
5240 MHz 48 20.0 dBm 20.0 dBm
5260 MHz 52 disabled 20.0 dBm (no IR, radar detection)
5280 MHz 56 disabled 20.0 dBm (no IR, radar detection)
5300 MHz 60 disabled 20.0 dBm (no IR, radar detection)
5320 MHz 64 disabled 20.0 dBm (no IR, radar detection)
5500 MHz 100 disabled 20.0 dBm (no IR, radar detection)
5520 MHz 104 disabled 20.0 dBm (no IR, radar detection)
5540 MHz 108 disabled 20.0 dBm (no IR, radar detection)
5560 MHz 112 disabled 20.0 dBm (no IR, radar detection)
5580 MHz 116 disabled 20.0 dBm (no IR, radar detection)
5600 MHz 120 disabled 20.0 dBm (no IR, radar detection)
5620 MHz 124 disabled 20.0 dBm (no IR, radar detection)
5640 MHz 128 disabled 20.0 dBm (no IR, radar detection)
5660 MHz 132 disabled 20.0 dBm (no IR, radar detection)
5680 MHz 136 disabled 20.0 dBm (no IR, radar detection)
5700 MHz 140 disabled 20.0 dBm (no IR, radar detection)
5720 MHz 144 13.0 dBm disabled
5745 MHz 149 13.0 dBm disabled
5765 MHz 153 13.0 dBm disabled
5785 MHz 157 13.0 dBm disabled
5805 MHz 161 13.0 dBm disabled
5825 MHz 165 13.0 dBm disabled

What is the reason for that and how can can I fix it?

There is a gist with the full output of iw and update log

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  • 1
    @Milliways The listed output is from iw reg get - and my setup is a stock RPI 3B+ or stock RPI 4B (behaviour is the same on both, so to me it does not really matter)
    – Sir Rufo
    Oct 4 '21 at 8:02
  • @Milliways My wifi works too, but not on the disabled frequencies as it does before and I had to change the freq at the Access Point to get it working
    – Sir Rufo
    Oct 4 '21 at 8:03
  • Same issues here in .at since the last Upgrade... :( Might this maybe also connected with bugs.debian.org/cgi-bin/bugreport.cgi?bug=985632 ?
    – JotZet
    Oct 4 '21 at 12:18
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Try running sudo apt update; sudo apt dist-upgrade -y; sudo reboot there's a brand new update to the WiFi firmware packages to resolve this failure.

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  • Yes, now it is back working as before
    – Sir Rufo
    Oct 4 '21 at 22:16
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It could be that DFS/TPC channels were disabled because they used to cause issues such as this one.

If you weren't affected by these problems, try getting WiFi chip firmware from an older Pi OS image. The files you need are located in /lib/firmware/brcm/, on my Pi 4 the brcmfmac43455-sdio.* files are used.

Changing the country might also help, but this may result in operating a non-compliant RF device, which, at least theoretically, could get you in trouble.

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