As possible workarounds in the meantime, can you open the server in Designer using ip address? Or open the db in client and then use View - Design to open in Designer?
Thanks for reporting.
Update: Have reproduced. I only see the connection failure when opening from the filtered server list, type partial server name in the server field. If the server is accessed by typing the full server name in the Server field and hitting [Enter], the connection succeeds and the server is opened. Do you see the same? Have submitted problem report VMAA89FP3F.