Performance Critical Bug:
Do not place conveyor belts off grid to filter funnels (leading out of chests).
This will cause the chest to output items infinitely because the range for the check for blocking the funnel (because there is an item in front of them) is smaller than the check to suck nearby items on to the conveyor belt. If you have spots were items coming out of a filter funnel are sucked on a full conveyor belt, fix it immediately.
I had this unnoticed for hours because I thought this was another quirky thing of the game. After a while I noticed how everything was incredibly slow (walking, crafting, conveyor belts) and thought this was because of the amount of items rendered. After finding out these spots (I had two), I had accumulated over 6000 single items on a single tile. This was because the spots were on my fuel line that automatically powers the iron and stone drills. It took me 45 minutes to put back all of the items.