Minecraft 1.16.4
Forge 35.1.28
WorldEdit 7.2.1+299386a

EDIT - After reopening the world the hoppers are loaded, therefore the hopper's are getting pasted, but the texture doesn't appear when pasted, I'll still consider this a bug and keep this issue open.

1. Image of the original structure -
   

2. Image after pasting -
   

This seems like nothing we can fix here, and isn't reproducible now.

I had something similar happen but with another modded block. What solved this is to move quite far away (maybe 1k blocks) so that the blocks unload and then go back into the same place.

I've semi-automated this process in my world by using a command block that sends you 1000 blocks in the +X direction, waits a bit, then sends you back to the original place.

If they're not appearing it's likely you disabled some //perf options or it's some sort of MC bug. Do you have a schematic we can use to reproduce?

I haven't fiddled with any perf options, everything is default, I'll post a schematic file ASAP.

Problem happens when pasting powered hoppers not just hoppers connected to chests, if you leave the game and rejoin should show up after.

Haven't had time to investigate, and also still don't have a schematic for reproduction purposes. Might look eventually, but won't mark accepted for now.

This issue has been automatically marked as stale because it has not been fully confirmed. It will be closed if no further activity occurs. Thank you for your contributions.

Marking this as help-wanted, not a high priority right now since it's just visual and that might not even be a bug on our end, but Minecraft's.

can confirm this is happening. if you take the item sorter, or attached schematic, and try stacking it, the hoppers going in to chests will not be copied through the stack. at least visually.

HOWEVER. as mentioned above, logging out and logging back in again will render the items correctly. on further testing, the hoppers are, in fact, extant, they simply are not rendering: you cannot enter the space where the hoppers would otherwise be 'located'.

item_sorter_slice.zip