Reply To: My Pi keeps showing offline after 20 idle minutes and wakes up when I SSH in

Screen blanking won’t do it. Classic Wi-Fi power saving on the Pi’s Broadcom chip, I had the same with a Pi 3B+ in a pump house. The Pi doesn’t sleep, the Wi-Fi does, and incoming packets get delayed or lost. Your paho client sends a ping every 60 s, the answer doesn’t come back in time, Hermetry sees nothing within the keepalive and closes the session, hence keepalive_timeout. Your SSH wakes the radio up, which is why everything comes back then.

Check it:

iw wlan0 get power_save
Power save: on

Turn it off for good on Bookworm with NetworkManager:

sudo tee /etc/NetworkManager/conf.d/wifi-powersave.conf <<EOF
[connection]
wifi.powersave = 2
EOF
sudo systemctl restart NetworkManager

(2 means disabled.) If you’re on an older image with dhcpcd, put iw wlan0 set power_save off in a script that runs after the network is up.

Also make your client reconnect on its own: client.reconnect_delay_set(1, 120) and loop_forever or loop_start, so a short drop fixes itself.