802.11 decryption not working properly

Hi all, I am working on some pentests in my home network using WPA2 and I am trying to sniff the traffic between the clients and the AP. Capturing data works like a charm with Wireshark, but WPA2 decryption seems not to work at all. Here is what I've done so far:

First of all, I sniffed some traffic I generated. To be more specific, Wireshark was running on one computer with wireless card in monitor mode (A), while I used another computer (B) to authenticate into the home network and after it received config from DHCP, I accessed the router's web UI.

My goal: In short, expected result of my work is to see some HTML code decoded from captured data.

Distance between devices A and B was less than a meter, while the AP was approx. 10 meters away, so I guess there was no communication left unheard. Since Wireshark sniffed a number of beacons and probes from my network and occasionally from some neighbors' networks too, I also guess the monitor mode works correctly.

Having traffic recorded as described I found the 4-way handshake packets. Wireshark recognizes them correctly and describes them as "Key (msg 1/4)", "Key (msg 2/4)", "Key (msg 3/4)" and "Key (msg 4/4)".

The problem: Although I have decryption enabled and WPA-PSK key set in IEEE 802.11 configuration, decryption doesn't work and I only see "802.11 Data" packets between computer B and the AP.

I tried to play with "Assume packets have FCS" and "Ignore the protection bit" settings, but I got only notices that all the packets are malformed. In another combination of these only first two key messages from 4-way handshake were recognized and in yet another combination all the "Data" packets were recognized as LLC (Logical-Link Control). I also tried different ways to enter the PSK into configuration (plaintext, percent-escaped characters, with and without SSID), but with no luck.

Is there anything I do obviously wrong? Thanks in advance for any help or hint.

Jirka