Access point with hostapd on ubuntu 20.04 server won't let clients connect

Question

I've got an ubuntu gateway server with 2 network cards, on for the internet and one for the lan. I've just set up the wireless access point on the wireless device using hostapd but the clients fail to connect to it with this error in the logs:

Dec 12 10:08:56 localhost hostapd: wlp6s0: STA 84:cf:bf:91:d8:35 IEEE 802.11: authenticated
Dec 12 10:08:56 localhost hostapd: wlp6s0: STA 84:cf:bf:91:d8:35 IEEE 802.11: associated (aid 1)
Dec 12 10:09:05 localhost hostapd: wlp6s0: STA 84:cf:bf:91:d8:35 IEEE 802.11: deauthenticated due to local deauth request

I have managed to put the configuration together so far pretty much by guesswork and finding individual steps in various places, because I couldn't find any how-to guide that covered ubuntu, netplan, and hostapd.

This is my setup:

hostapd.conf:

adam@gondolin:~$ cat /etc/hostapd/hostapd.conf 
interface=wlp6s0
driver=nl80211
bridge=br0
ssid=Anduin
hw_mode=g
channel=1
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
wpa=3
wpa_passphrase=secret123
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP
rsn_pairwise=CCMP

netplan:

adam@gondolin:~$ cat /etc/netplan/01-netcfg.yaml
# This file describes the network interfaces available on your system
# For more information, see netplan(5).
network:
  version: 2
  renderer: networkd
  ethernets:
    enp5s0:
      dhcp4: yes
      dhcp6: yes
    eno1:
      addresses:
      - fe80::10/128
      - 192.168.0.3/24
      dhcp4: no
      dhcp6: no
    wlp6s0:
      dhcp4: no
      dhcp6: no

Answer 1

Still no clear idea about why the deauth messages appeared, but I solved the hostapd issues by setting up the bridge in netplan.

adam@gondolin:~$ cat /etc/netplan/01-netcfg.yaml
# This file describes the network interfaces available on your system
# For more information, see netplan(5).
network:
  version: 2
  renderer: networkd
  ethernets:
    enp5s0:
      dhcp4: yes
      dhcp6: yes
    eno1:
      dhcp4: no
      dhcp6: no
    wlp6s0:
      dhcp4: no
      dhcp6: no
  bridges:
    br0:
      interfaces:
        - eno1
        - wlp6s0
      addresses:
        - 192.168.0.3/24
      nameservers:
        addresses: [208.67.220.220,208.67.222.222]
adam@gondolin:~$