I'm guessing here, that that's where the bottom overlap finishes, so the rail is stiff, but the deck is flexing, creating that crack.
the foam underneath may or may not be damaged. If it's not damaged, you just need to spread the load on that flex point.
No superficial fix will work for more than about 5 minutes, there's a lot of movement on that fine line. you have to kill that movement first.

The pad will need to be rolled back, the damaged area sanded back to the underlying foam and then be restored, stronger than the original.
Otherwise it will just keep cracking.

Yeah a bit soft under the pad