I've noticed in the farming spots where enemies respawn regularly, there are times where it activates a "horde" mode of sorts. Where countless enemies spawn in constantly with no stop for about 5 minutes. Ranging from weak to powerful enemies. This usually results in huge ammo and engram drops. My curiosity of this is was this a planned event and if so what are the exact triggers to start it? When playing on Mars we were looking for chests in Patrol and entered the circular valley where the Vex and Cabal spawn at the very beginning. After about 20 min of chest hunting we activated the horde mode and died about 2 minutes in. A few days later I was at the Venus farm spot where again another horde mode activated. We survived this time and collect about 10 engrams each and many Grimoire upgrades. But when we went back to the Mars spot, we couldn't get the horde to activate after over 30 min of trying. My brother said he even had a horde at the Cosmodrome farm spot one time. Any info to help with these "horde" mode events will be helpful.