Updated description by GoldenHelmet June 5, 2020

Steps to reproduce

1. Build a trough 9 blocks long using full blocks on the bottom and sides.
2. Place a water source at one end of the trough.
3. Drop items into the water source.

Expected result

Items travel to the end of the water flow at uniform speed.

Actual result

Items travel at uniform speed through the first 5 blocks of flowing water, then travel more slowly through the final 2.

Original description

When the items in the 2 block below the end of water the items speed will suddenly slow and then items arrived to end of water the items will getting visual glitching.