I'm making a sorting system using the item router to filter the items. It contains about 12 Item Router in sequence (see https://i.imgur.com/YUx2nga.png).

When an item enters the fist Item Router, it takes so much time to finish filtering, other chests don't open, blocks don't break, mobs don't take hits, etc.
I don't know if all Item Routers try to filter in the same update cycle or something like that, but it would be cool if you guys could improve that.

Awesome mod! Thanks.

A screenshot that shows the important parts of the setup would be helpful. Maybe create a creative superflat world in singleplayer and build a setup with this issue there?
Edit: What exact version of IE do you use? There are quite a lot of IE builds for 1.12.
Edit 2: A long chain of routers did not cause lag in my tests. I found a different setup with a lot of lag though, I'll see whether I can fix it in that case.
Edit3: No idea what I did wrong with my long chain, it causes/caused insane lag in later tests. Fixed now.

I'm using the 0.12-85 version.
I tested it in the superflat, my conclusion was to disable the filter by oredictionary and remove the unused Item Router for the time being. Now the chain of Routers is minor and there is almost no lag.
Basically before my rough fix, it was literally a chain of Routers and all of then was like this: https://i.imgur.com/cNlPRtQ.png