I've grinded in the same spot for a long time and it's definitely not coz of my kill rate or location. It was always something to do with the channel. In my usual spot, I'm able to grind properly without downtime if I see a lot of people around in the same channel, but if the channel is low populated (I can confirm this coz I run around and look when ever it stops spawning for me) my character waits around some where between 30-40secs before a mob spawns.
Sometimes when it stops spawning, I go to a more populated channel and see that the same spot spawns mobs perfectly.
I can agree different spots have different dense of mobs but the issue I'm talking about has nothing to do with it 100%