Unfortunately, most connectivity problems arise on the Host side rather than on the Viewer side. If you cannot access a remote Host this means that the Host has issues connecting to our intermediary server. This might be caused by a number of reasons, such as antivirus software update that blocks the Host, the Host service hanging or not working properly or the Host installation being corrupted for some reason.
It's unlikely that you will be able to troubleshoot the issue while on the Viewer side. You'll need to get to the Host side anyway.