Probably due to the fishing minigame. Out of all of the spots I've seen, barely any chest spawns near a water source where people fish at.
(btw, did it go high with all players enabled or were they disabled?)
Well obviously with players enabled I knew that would have great effect on it
So I turned them all off
It still happened
Second don't forget about your favourite fishing spots
In the fountains that was actually the place where it spiked up to 5K
near the rest of the ocean the most I really remember was 2-3K