The requests for control.html are used to issue subscription requests.
You can find multiple requests in a few seconds, but the arguments should be different.
You could see multiple requests with the same arguments in case something is slowing down the network or Server processing; in this case, the client may reissue requests for which it hasn't received any answer.

The web client library tries to collect multiple subscription requests
that are issued by the pages nearly at the same time,
into a single control.html request.
Hence, subsequent control.html requests should be separated by a short time interval.