Network-Manager and Fritzbox

[Jürgen Bausa <Juergen Bausa online de>]

I am running a laptop (Xiaomi Air 12) with debian Buster AMD64 and use KDE 
with network-Manager.
Wifi is supplied by a Fritzbox 7530 wifi-router (2.4 and 5 GHz with same ssid 
and wpa2).
Since I use the Fritzbox (before that I used a TP-Link router, that did not 
have this problem)
I experience the following problem:

When a new connection is initiated by the laptop (after reboot or resume) in 
some cases (about 5-10 %)
the connection is made for a very short time only. The laptop is then 
disconnected and a window appears
on the desktop, saying that the password had been wrong (which is definitely 
not the case: the correct password
is stored in NMs database) and asking for the correct one. When I type in the 
correct password,
the connection is made. Or, if I just close the window and clcik on the 
connection in NM, the
connection is also made.

This is what I find in the routers log (lina is my laptop):
(translation from german).

20.12.19 22:57:51 WIFI-device has been disconnected (5 GHz), lina, IP 
192.168.0.31, MAC XX:XX:XX:XX:XX:XX.
20.12.19 22:57:48 WIFI-device has been connected, WIFI reactivated with full 
power (5 GHz).

These two things are always the same, when the problem happens:
- the router resumes from power saving mode when the first attempt to connect 
is made (WIFI reactivated with full power)
- 5 Ghz is used

This is what I find in the laptops log:

wlp1s0: CTRL-EVENT-REGDOM-CHANGE init=DRIVER type=COUNTRY alpha2=DE
wlp1s0: SME: Trying to authenticate with XX:XX:XX:XX:XX:XX (SSID='meineSSID' 
freq=5220 MHz)
wlp1s0: Trying to associate with XX:XX:XX:XX:XX:XX (SSID='meineSSID' freq=5220 
MHz)
wlp1s0: Associated with XX:XX:XX:XX:XX:XX
wlp1s0: CTRL-EVENT-SUBNET-STATUS-UPDATE status=0
wlp1s0: WPA: Key negotiation completed with XX:XX:XX:XX:XX:XX [PTK=CCMP 
GTK=CCMP]
wlp1s0: CTRL-EVENT-CONNECTED - Connection to XX:XX:XX:XX:XX:XX completed [id=0 
id_str=]
wlp1s0: CTRL-EVENT-SIGNAL-CHANGE above=1 signal=-70 noise=9999 txrate=6000
Dec 20 22:57:48 lina avahi-daemon[637]: Joining mDNS multicast group on 
interface wlp1s0.IPv6 with address fe80::31a:e3aa:b668:28ed.
Dec 20 22:57:48 lina avahi-daemon[637]: New relevant interface wlp1s0.IPv6 for 
mDNS.
Dec 20 22:57:48 lina avahi-daemon[637]: Registering new address record for 
fe80::31a:e3aa:b668:28ed on wlp1s0.*.
Dec 20 22:57:49 lina dhclient[17036]: DHCPREQUEST for 192.168.0.31 on wlp1s0 
to 255.255.255.255 port 67
wlp1s0: CTRL-EVENT-DISCONNECTED bssid=XX:XX:XX:XX:XX:XX reason=2
wlp1s0: WPA: 4-Way Handshake failed - pre-shared key may be incorrect
wlp1s0: CTRL-EVENT-SSID-TEMP-DISABLED id=0 ssid="meineSSID" auth_failures=1 
duration=10 reason=WRONG_KEY
dbus: wpa_dbus_property_changed: no property SessionLength in object /fi/w1/
wpa_supplicant1/Interfaces/5
wlp1s0: CTRL-EVENT-REGDOM-CHANGE init=CORE type=WORLD
Dec 20 22:57:54 lina systemd[1]: NetworkManager-dispatcher.service: Succeeded.
Dec 20 22:58:06 lina avahi-daemon[637]: Withdrawing address record for 
fe80::31a:e3aa:b668:28ed on wlp1s0.
Dec 20 22:58:06 lina avahi-daemon[637]: Leaving mDNS multicast group on 
interface wlp1s0.IPv6 with address xxxx::xxxx:xxxx:xxxx:xxxx.
Dec 20 22:58:06 lina avahi-daemon[637]: Interface wlp1s0.IPv6 no longer 
relevant for mDNS.
wlp1s0: Reject scan trigger since one is already pending

The whole thing only happens with the debian buster laptop. No problem with 
other clients (android, Mac, iphone, Windows10)

I tried this in another house, where same router is used. There, the same 
problem appears. However with a different
laptop (Acer),  but also debian buster AMD64 with KDE and network-Manager.

Anyone else using a Fritzbox Router? Having or not having this problem? I am 
not sure if it is related to router, NM,
or kernel. I dont think its related to the wifi driver, because it happened on 
two laptops with different hardware.

Is there any way for me to obtain more information do debug this?

Regards,

Jürgen