The WaitOne calls in which the reported threads are stuck are supposed to have a short life. The involved monitor is used to wait for the outcome of a connection attempt and it is released after the connection attempt has completed with either success or failure.

When I try keeping the response blocked on the Server and closing the browser, it still closes immediately, though the process remains alive for a few seconds more.
Is that the issue you are reporting or, in your case, does the browser stay alive forever?
Otherwise, may you please help us replicating the issue?