I do have similar problems since V6 although using actual Versions 6.07 for hosts and viewer and 603 for private server.
For example the host is online and also online is shown in viewer but if connecting it switches to offline although being physical online. Or it is showing offline but if connecting it jumps to online.
I do have many interruptions while working on hosts, if connecting again it takes 2 or more trials to get connection again.
In viewers Log I have many errors like
CheckID Connection. After process message. Host "xy:55655". MsgCode: 10
or socket errors like "EIdConnClosedGracefully".
So I seem to be the only one with this troubles, can you help me to find a solution?