Using commands to adjust an arrow or trident's Motion value once to accelerate the arrow causes it to appear as though it's flying in a slightly offset direction than where it actually lands.

How to reproduce:

For the following steps, replace all instances of arrow with trident to test the issue with tridents.

1. Execute the following command:

   /scoreboard objectives add flying_timer dummy

2. Place a repeating command block set to Always Active with the following command:

   /scoreboard players add @e[type=arrow] flying_timer 1

3. Place another repeating command block set to Always Active and two chain command blocks set to Always Active chained to the repeating command block, with the following commands in them respectively:

   /execute as @e[type=arrow,scores={flying_timer=1}] store result entity @s Motion[0] double 0.0002 run data get entity @s Motion[0] 10000

   /execute as @e[type=arrow,scores={flying_timer=1}] store result entity @s Motion[1] double 0.0002 run data get entity @s Motion[1] 10000

   /execute as @e[type=arrow,scores=\{flying_timer=1}] store result entity @s Motion[2] double 0.0002 run data get entity @s Motion[2] 10000

4. Shoot an arrow.

Expected result:

The arrow or trident would fly in the direction as the block it's about to hit.

Observed result:

The arrow or trident flies in a slightly offset direction, but ends up at the correct location when landing.