items and mobs are not despawning when they are left in unloaded chunks or not in the players ticking area. passive mobs have problems spawning or next to none and any items left in unloaded chunks cause a lot of frame rate issues. I did run a few tests my self i left a cow in a 20 x 20 area and no way out, i then went 1000 blocks away and even turn render to 6 chunks and waited well over an hour and came bk to find the cow was still there. i should just say i made the floor from slabs. and i did the same with the items and they were still there to. I thought it was 5 mins for items and 30 seconds for mobs