Sonoff s31 mDNS not working when plugged into AC

Hardware
1

i have an sonoff s31 switch that worked wonderfully until it didn’t this past week or so. i noticed that it disappeared off esphome and my apple home bridge via homeassistant. so i try flashing it again using usb → uart and after disconnecting and connecting 5v power it seems to work just fine, i can ping its mDNS address and control it via HA. but when i put it all back together and plug it into the wall, it stops responding to mDNS and i can’t control it via HA. it is connected to wifi because i see it in unifi console and i can ping the ip address directly.

i also bought a brand new one off amazon and same behavior.

any ideas?

    esphome:
        name: laundryroom-light-switch
        friendly_name: laundryroom-light-switch

    esp8266:
        board: esp01_1m

    # Enable logging
    logger:

    # Enable Home Assistant API
    api:
        encryption:
            key: "f"

    ota:
        password: "f"

    wifi:
        ssid: !secret wifi_ssid
        password: !secret wifi_password

        # Enable fallback hotspot (captive portal) in case wifi connection fails
        ap:
            ssid: "Laundryroom-Light-Switch"
            password: "f"

    captive_portal:

    uart:
        rx_pin: RX
        baud_rate: 4800

    binary_sensor:
        - platform: gpio
            pin:
                number: GPIO0
                mode: INPUT_PULLUP
                inverted: True
            name: "Sonoff S31 Button"
            on_press:
                - switch.toggle: relay
        - platform: status
            name: "Sonoff S31 Status"

    sensor:
        - platform: wifi_signal
            name: "Sonoff S31 WiFi Signal"
            update_interval: 60s
        - platform: cse7766
            current:
                name: "Sonoff S31 Current"
                accuracy_decimals: 1
            voltage:
                name: "Sonoff S31 Voltage"
                accuracy_decimals: 1
            power:
                name: "Sonoff S31 Power"
                accuracy_decimals: 1
                id: my_power

    switch:
        - platform: gpio
            name: "Sonoff S31 Relay"
            pin: GPIO12
            id: relay
            restore_mode: ALWAYS_ON

    time:
        - platform: sntp
            id: my_time

    status_led:
        pin:
            number: GPIO13
            inverted: True
2

Can you ping with the (non mdns) hostname?

Do you use any vlans by chance? I think this unifi hardware blocks mdns broadcast across vlans…

You can also use esphome without mdns (see esphome faqs)

3

Latest firmware update is breaking my Sonoff S31s.
Sometimes they will time out connecting to wifi and I have to connect to them to set wifi. Even when they do connect they don’t work. When I look for the logs at best it will say “Successfully connected”
but then
“WARNING Can’t connect to ESPHome API for sonoff-s31-02 @ 192.168.1.2: Timeout waiting for HelloResponse, ConnectResponse after 30.0s (TimeoutAPIError)
INFO Trying to connect to sonoff-s31-02 @ 192.168.1.2 in the background
WARNING sonoff-s31-02 @ 192.168.1.2: Connection error occurred: sonoff-s31-02 @ 192.168.1.2: Connection lost”

I had an old firmware from November for a different S31 and was able to flash that to the problem S31 and it works fine.