I can happily state that I had no DS issues of the "bad kind" (hard to resolve, generic or systemic problem type) for a few month now.
No need to specify that I was very happy with this state of play, thanks to the release of DS 6.9 SP3! But has it happens, there's always a time when new problems are found, or old ones crop back up one way or another. So I'm back onto the classic Aclient / DAgent -> DS connectivity issue.
I'll take this opportunity to refresh my brain on how DS handles communications to the clients (... off to Google Doc to create a diagram for this -> back from Google doc, got the png files attached below).
This is only a very rough overview that shows which elements in the communication chain are creating log files.
From the AClient (or DAgent) up we have the Aclient.log generated on the client itself, the Communication Logs on the server, where communication between a single computer and the DS is recorded on the server and the axengine which records message handling request and processing as well as scheduling information etc.
Note that the session state of the DS agents is kept on the dbo.Sessions table in the eXpress database.