On our Spigot server we have noticed a problem where the item transfer of hoppers is being slowed down when there is a big load of hoppers. For example, we have a big sorting system containing close to 1k hoppers. When there are only a few items being sorted, the item transfer is still at 2.5 items per second. However, when the sorting system has to sort out large quantities of items, that is when the item transfer speed can go as low as 0.3 items per second. The hopper timings are changed for the whole server, not just around the sorting system

Slowing down the transfer speed seems to be intentional, cause the tps of the server always stays above 19.5, even when the sorting system is under heavy load. At the same time this causes a problem with redstone. When someone actively uses their sorting system and all hopper transfer speeds are slowed down, that means that redstone contraptions that include hoppers are no longer reliable.

Especially the redstone part, that is a feature that is no broken/unreliable.