After Upgrading from 19.07.8 to version 21.02.0 the 5 GHZ WLAN is not working any more.
The WLAN gets shutdown by DFS.
FYI: Same freqency was used (channel 52) on 19.07.8 - worked perfekt, on 21.02.0 - doesn't work due to radar detect and shutdown by DFS.
I observed similar symptoms for 5G wireless on my TL-WDR4300 v1 after upgrading from 19.07.x to 21.02.1
Clients barely connected to 5G wireless
The "local interface" was not shown in the 5GHz channel analysis chart
daemon.notice hostapd: wlan1: interface state DISABLED→COUNTRY_UPDATE
daemon.notice hostapd: wlan1: interface state COUNTRY_UPDATE→HT_SCAN
daemon.err hostapd: could not get valid channel
daemon.notice hostapd: wlan1: interface state HT_SCAN→DFS
The issues disappeared here after upgrading the wireless-regdb package to 2021.08.28-1.
daemon.notice hostapd: wlan1: DFS-CAC-COMPLETED success=1 freq=5600 ht_enabled=1 chan_offset=-1 chan_width=2 cf1=5590 cf2=0
aemon.notice netifd: Network device 'wlan1' link is up
daemon.notice hostapd: wlan1: interface state DFS->ENABLED
daemon.notice hostapd: wlan1: AP-ENABLED