I found out this line:
LOG_INF("Received %i data %s from: %s", len, data, log_strdup(addr));
Without this its working but i had another error here (caused by my try and arror):
This is the right code:
if (strncmp(data, "&I", 2) == 0 )
{
buf = k_malloc(sizeof(*buf));
iCounter++;
LOG_INF("&I %i", iCounter);
buf->len = sprintf(buf->data, "&I %i\n", iCounter);
k_fifo_put(&answer_buffer, buf);
}