Thought I would leave some feedback here in case anyone else has the same issue with their new Fenn paddle...
Turns out the problem was that the lever wasn't set up correctly and as a result, there wasn't enough friction created when tightening the lever to hold it (or the paddle) in place. I found this out the hard way on a rather hectic paddle after work yesterday.
To set the lever up correctly, there are two small screws on either side of the adjusting screw that hold the adjusting screw in place, that need to be loosened. Once loose, the adjusting screw can be tightened to give the correct friction, then the two retaining screws tightened again.
Fennix Swordfish S - Carbon Hybrid