No, I've seen the performance logs. It is GC. When the machine hits the limits it goes off and does serious GC, ie, not incremental but full.
Sometimes it also has to run out and kill off background tasks which seems to be time consuming. Does it wait for them to exit or something? KILL -9!
Many Android apps hits this problem when scrolling because they're dropping lots of objects from use and creating new ones. Then to fix that leads them into crazy object reuse schemes which start to make C++ look quite nice.