I think the fact it's the wrong bolt. Need to get something on the arch side as well. That's been "fixed" as original bolt has snapped I reckon.
That piece of threaded bar sticking out isn't the original design intent. This is;
Is the joint loose?
It's no real different to the normal bolt but it looks like it's possibly rusted?
Best bet is to undo and get a big thick washer in between the mount and strut.