1.13.2 Items skipping over hoppers in Paper (does not happen in Vanilla)

Hello, I am trying to troubleshoot an item sorting system that is not working as intended with a 1.13.2 PaperMC SMP server. I have used world edit to create a schematic of the build that I then tested in a vanilla single player 1.13.2 server. On vanilla testing, the sorter works 100% of the time.

Items are carried via water streams across hoppers that use the generic ImpulseSV style item sorting circuit. The problem occurs when not all of the items get picked up by the correct hopper. On the vanilla server, the items are all picked up by the hopper.

From an input chest, the items travel through hoppers to a dropper that shoot them up a water elevator, where they are moved across the item sorting hoppers. At first, I adjusted item drop radius to 0 because I realized the items were merging after being shot out of the dropper into the water elevator. Then I noticed that if I moved to another part of the sorting system, the item entities would be deloaded (which did not happen in Vanilla testing). So, I adjusted entity-activitation-range to 32, which made the items load similarly to Vanilla.

After making these changes, the hoppers are now picking up a majority of the items. However, a few of the items still seem to move too quickly past the hoppers before they can be picked up. I was wondering what differences there still exist between Paper and Vanilla that could cause this behavior. I noticed there are several hopper related config settings (i.e. Hopper Transfer: 8 Hopper Check: 1 Hopper Amount: 1), but I’m not sure if these would change anything. I do not want to break other redstone contraptions on the server.

Additionally, I have watched the count of items in the hoppers as the items get passed by, and the hoppers themselves are never full. I have attempted to increase the space between water streams using trap doors and ice, but it did not work, and there is not enough specifically around corners to slow the items down enough. The TPS of the server never drops below 20 during testing. Thanks for any help you can give.

Server plugins (I have changed very little of the configs of these):

I’m having this same issue on 1.14.4.

Did you find a fix?

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For what its worth 3 months after your post.

Hopper Transfer: 8 is the amount of gameticks the hopper is in cooldown after pulling or pushing an item. This could be the problem with your sorter. If the hopper picks up a stack it will push them all out into the chest or whatever. After the last pushing action the hopper still needs 8 ticks to cooldown and isnt able to pick up the next stack. TPS does influence this, but you stated its always 20 so that shouldn’t be the problem.

Hopper Check: 1 I think the amount of ticks needed to check for items to push or pull.

Hopper Amount: 1 Amount of items to be pushed.

I noticed the same thing with my water stream item sorter. Slowing the items down alot helps but didnt entirely solve it. I also pushed the items out in batches with a little delay between each batch so the hopper has time to push everything out and cool down. Also I noticed that when building a multi item sorter (Tange Tek style) that the hoppers on a paper server behave a bit differently. I needed to set the clock about twice as slow for it to work. I’ve tried multiple of those type of sorters and they never worked until I figured out the thing with the clock.

My guess is that hopper behaviour is a bit slower on a paper server than on vanilla.