I tried to cancel a discussion which I discovered I couldn’t make. LingQ wouldn’t let me because it was part of a course. So I cancelled the course (or at least that particular set of times for the course). Then I found that the discussions which belonged to the course were still on my calendar! I still had to delete the discussion I can’t make, and my schedule has three course-related discussions left on it that are no longer part of a course. Is this right? The session in question was Mon 12th Jan and the following 3 Mondays at 12pm GMT.
Yes, that is correct. We are unable to cancel the conversations all at once. In effect, a session is a way of creating and grouping conversations but the conversations have to be canceled individually. As you say though, they can’t be canceled until after the session has been canceled.
A little inconvenient but that’s the way it is…a disincentive to cancel sessions! 
Okay Mark, I can cope with cancelling the session then cancelling the one discussion that clashes with, say, my dentist’s appointment. That’s easy enough.
The hard bit for me is working out which session the discussion is a part of. I have created several courses with similar content and I have to work through each one to find which one the discussion I’m trying to cancel is part of! When I get the error message saying “you can’t cancel this discussion because it is part of a group course” it would be very helpful if it gave me the title of the course, or even better, a link to it, so I can go straight there and cancel that session.
I hear you, Helen but there isn’t much we can do for you right now. You’ll just have to go by Conversation time and title as you’re doing now. I will add this to the list but it will be a while. Sorry about that.
You have your priorities Mark, and the ease of use for students comes first!
I expect there is a way I can get more organised 