I found the cause of this and posted a bug report :

https://github.com/espressif/esp-idf/issues/3957

The vTaskDelay should only be suspending the current thread and spacing out the sending, the reply events come from other threads handling the TCP stack etc. The vanilla example sends a message once a second so the problem I am seeing is hidden. It's when one tries to send messages more frequently t...

I came across the problem with my own application and server but can reproduce the same situation by making minor changes to the example provided in the esp-idf SDK found at examples/protocols/websocket using the default ws://echo.websocket.org service. change while (i < 10) { if (esp_websocket_clie...