It looks like you do not have explicit memory allocations in your code, which means it happends some other way – I see you use some third party libs.
You could try taking a memory snapshot before and after GC (goto devtools: memory, push the red button).
Snapshots have class names, count of objects of those classes and the memory size taken.
So you get 2 snapshots, calculate a diff (somehow), and see if it fits to this saw-shaped picture you have.