Just wanted to say that indeed there is a problem with viewer 6.8 just as you describe. We are currently investigating it and testing different solutions.
Since it's a problem on the Viewer side the Host logs won't help us much. They can only confirm that the problem at hand is not the Host's, but the Viewer's.
But you can still help us figure out this problem if you send us the Viewer log (use support@). The log should preferably capture the moment when the connection is going offline/online. Along with the log, please, also send us your license key (even if it's a free license key) - this will help us properly identify the connection in our server logs.
The log looks ok - it seems that the Host successfully establishes connection to your server and is ready for connection.
I'm afraid that the connectivity (network) issue might be on the Viewer side. You should check if the Viewer PC can communicate with the server PC and if the connection is stable (you can try the ping -t command, for example).
This is very unusual. The only program setting remotely related to what you describe is "Lock workstation on disconnect" property (connection properties -> additional properties).
But since you say that locking happens on connect rather than on disconnect, and that it is really Remote Utilities' own Full Control mode rather than the RDP, we don't really know what might the reason. This is the first time we are reported such behavior.
One possible explanation could be that there is security software on your computer that prevents remote connection and/or input emulation typical for remote control software.