Possible Memory Leak?
The first request at 3:20 caused some memory to be held, but notice that the GCs after the second request reclaimed most of it. Also I think that major GC was performed only after the second request at 4:40.
It looks like there is no leak. My theory is that the request at 3:20 caused the young generation to fill up, and the resulting minor GC promoted some objects to older generation. The next major GC, caused by the request at 4:40 cleaned most of those up.
You can verify this by using a profiler to mark the heap before issuing the same request as the one at 3:20, forcing a full GC, and then checking what objects are lingering. I am not sure if VisualVM lets you (1) mark the heap and (2) force a full GC, but OptimizeIt used to do it.