I previously had this issue. It only affects admins who have the rights to change the order of the pinned topics which is why it's unlikely others can't reproduce on the OPs site.
However since 1.7 (could be Chrome 64) I no longer have the problem.
Those errors usually mean websockets are not proxied correctly, make sure your nginx setup is correct. If you are using cloudflare you need to disable acceleration. They don't support websockets on smaller plans.