If you have already tried the Registry parameter "TCPFinWait2Delay", there is no other user-defined setting that I am aware of to control it.. I believe the default in Windows was 240 seconds, we recommend lowering that to 30-45s generally.
When your AV is running, do those connections close after ~240 seconds?
Which AV is the culprit for you?
You may want to try disabling your AV's "internet" monitoring, so that they do not monitor web pages and downloads, this may help.
Thanks for writing, sorry I can't be of more help.
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