If you analyze how minecarts move by doing /tick freeze and then incrementing tick by tick you will see the minecart movement is not consistent.
Sometimes it moves a little, sometimes a lot, sometimes it stays in place.

Reproduction Steps

• Build a long track for a minecart
• Do /tick freeze and /tick step 1t to observe how the minecart behaves

Observed Results

• The minecart sometimes fails to move. Other times it moves by varying ammounts

Expected Results

• The minecart would move by a predictable amount determined by it's bpt (blocks per tick) velocity

Videos

Here's the issue at low (default) speed
inconsistency_default_speed.mp4

And here it is at a high minecartMaxSpeed value
inconsistency_high_speed.mp4