Why can the camera return the error "Invalid session in request data!"?

Question

PHP

The problem is that the error occurs every time
there is a Dahua HDW2230TP-AS-0280B camera. I make a backup copy of the video to my server every 10 minutes. The request looks like this:

# шаг 1.  curl запрос на создание задачи (id)
$task = reqCam("$urlcam/cgi-bin/mediaFileFind.cgi?action=factory.create");
$id = explode("=",trim($task))[1]; // обрезание ID
# шаг 2. установка поиска видео по заданным $start и $end значениям
reqCam("$urlcam/cgi-bin/mediaFileFind.cgi?action=findFile&object=$id&condition.Channel=1&condition.StartTime=$start&condition.EndTime=$end&condition.Types[0]=dav");
# шаг 3. отображение списка видео
$listvideo = reqCam("$urlcam/cgi-bin/mediaFileFind.cgi?action=findNextFile&object=$id&count=100");

And this code can show about 10 (sometimes more) errors of this kind for 100 iterations:

{"error":{"code":287637505,"message":"Invalid session in request data!"},"result":false}

the error occurs in the second step when I set the search parameters. I can't find any patterns.

How can you fight it?