Hmm, this is very interesting for me. This hasn't happened to me a lot, but it has happened to me before. I have a couple thoughts why this may be happening. I don't know too much about how the game works in code, but bare with me.

-Maybe a rendering issue? The game may keep a location on the map rendered even when the player has already past the location it's rendered, taking up memory, demanding more?

I don't know, but that's what I'm thinking. Don't other games render new locations and just unrender the old rendered location(s)?

EDIT: Maybe it's also because of players joining the server or map. More people, more demand.