How to find out the cause of a (massive) paint in chrome dev tools?

I'm working on a game. The map size in pixels is 30720 x 30720.This Paint call of 16.7 M x 16.7 M pixels seems a bit excessive and is causing a massive drop in fps.

Usually the paint calls look quite sensible, a couple of pixels in a location within the viewport (ie, updating sprites or a piece of game UI)

In this case though, don't have a clue what piece of code is responsible for this massive paint. How would I go about finding that out?