In the early stages async web sockets definitely had many issues. I had many similar issues when trying the ..ShareConnection=1 in 2015.1.2 and as you mentioned, synced web sockets worked fine. I contacted WRC and they advised me to upgrade to 2017.1.2. Upgrading to 2017.1.2 fixed all the issues I had, so not sure what the exact problem you have is but upgrading might be the only solution.