955i SSSA chain tension going wrong/loose?

Has anyone else had issues with the SSSA losing its chain tension?
Specifically I haven't needed to adjust my chain for some time, though have been keeping an eye on it, cleaning and lubing it. Went for a short ride today and could hear the chain clicking. The chain was totally taught with zero slack! Was definitely ok, a couple of days ago. I actually road the 10 miles home sitting on the tank so not to put too much strain on it!

I'm not entirely sure and haven't looked at it properly yet, but I'm wondering if the open end of the thread has got some crud in it preventing it from being tightened all the way. The bolt was done up tightly and was tight to undo so hadn't come loose. Have now put an extra washer on the bolt and it did feel like it was squeezing the clamp together this time, as opposed to just coming to a stop.

Could only find limited information on this, so don't know if many others have ever experienced the same thing. Did find this example: Self tightening drive chain SSSA - Problem Solving - Tech Forums - Messageboard - Triumph Torque