ESP01 + relay module - delay

[citerkoo]

Hello,

I am using a 2 channel relay module (http://www.chinalctech.com/xwzx/24.html) with ESP-01 to control the relays. I have uploaded a custom code to ESP-01. ESP-01 is supposed to connect to my WiFi, start a HTTP server and wait for requests. Based on the HTTP request received, it should switch the relay by sending message using UART to the relay module board.

Everything works, however there is a ~10 seconds delay between HTTP request received and relay phisically switched.

The ESP-01 should not be a problem - it sucessfully accepts the HTTP request, sucessfully sends a HTTP response (in 100ms) and also the blue UART TX LED blinks with no delay, which means, that the message to the board has been send right away.

When I put the ESP-01 to USB debugger, I can see the correct serial messages also with no delay.

The input voltage is steady 5V.

What might be the reason that the module reacts with 10s delay?