Could not add STA to kernel driver

[Marek.Floriańczyk]

Hi

I have a question.  I have Debian Buster with hostapd 2.7 from packages. I 
would like to run AP with 80 devices connected to it without any encryption, 
at the bottom there is my configuration file.

The problem is that after 11 devices has been connected, I can see in hostapd 
logs this message:
wlp3s0: STA 4c:11:ae:f9:a0:fc IEEE 802.11: authenticated
wlp3s0: STA 4c:11:ae:f9:a0:fc IEEE 802.11: associated (aid 11)
wlp3s0: AP-STA-CONNECTED 4c:11:ae:f9:a0:fc
wlp3s0: STA 4c:11:ae:f9:a0:fc RADIUS: starting accounting session 
7D19D5A198595E57
wlp3s0: STA 4c:11:ae:f9:7c:e4 IEEE 802.11: Could not add STA to kernel driver
wlp3s0: STA 4c:11:ae:f8:ee:fc IEEE 802.11: Could not add STA to kernel driver

I have kernel
vmlinuz-4.19.0-10-amd64

Debug from dmesg about wifi module:
[    7.276894] Intel(R) Wireless WiFi driver for Linux 
[    7.317193] iwlwifi 0000:03:00.0: firmware: direct-loading firmware 
iwlwifi-3168-29.ucode 
[    7.318027] iwlwifi 0000:03:00.0: loaded firmware version 29.1044073957.0 
op_mode iwlmvm 
[    7.516613] iwlwifi 0000:03:00.0: Detected Intel(R) Dual Band Wireless AC 
3168, REV=0x220 
[    7.548539] iwlwifi 0000:03:00.0: base HW address: d4:3b:04:51:69:e0 
[    7.670030] iwlwifi 0000:03:00.0 wlp3s0: renamed from wlan0

My computer is Udoo x86 with this wifi module:
https://shop.udoo.org/kit-m2-wifi-bt.html

hostapd.conf
# 
# nl80211 mode 
# 

ssid=fmcode 
interface=wlp3s0 
hw_mode=g 
channel=5 
#bridge=br0 
driver=nl80211 

logger_syslog=1 
logger_syslog_level=1 
wmm_enabled=0 
wpa=0 
preamble=0 

#wpa_psk=
#wpa_passphrase=
#wpa_key_mgmt=WPA-PSK 

#wpa_pairwise=TKIP 
#rsn_pairwise=CCMP 
#auth_algs=1 
#macaddr_acl=0 

#noscan=1 

### IEEE 802.11n 
#ieee80211n=1 
#ht_capab= 
#country_code=US 
#ieee80211d=1 
### IEEE 802.11n 

### IEEE 802.11a 
#hw_mode=a 
### IEEE 802.11a 

### IEEE 802.11ac 
#ieee80211ac=1 
#vht_capab=[MAX-MPDU-11454][SHORT-GI-80][TX-STBC-2BY1][RX-STBC-1][MAX-A-MPDU-
LEN-EXP3] 
#vht_oper_chwidth=1 
#vht_oper_centr_freq_seg0_idx=42 
### IEEE 802.11ac 

# controlling enabled 
ctrl_interface=/var/run/hostapd 
ctrl_interface_group=0

#End

Any idea why only 10 devices can be connected. Actually I have the same issue 
on my laptop with different hardware.

Best Regards
Marek