Bug setup and replication (the file was too large to attach): https://youtu.be/cze1-EZYyX8

minecartMaxSpeed in the video is set to 1000. I have tested at lower speeds (one of the attached screenshots shows that the minecartMaxSpeed is set to 25 and the bug still occurs) with similar results.

The number of rails (and type) matter because the minecarts' speeds differ with different rails.

In the box in the video, I have a powered rail, but this can be replaced with a different rail (I found it to take longer for the minecarts to get stuck when I did a rail other than an unpowered powered rail)

Steps to reproduce:

1. Import and open the attached world: world.zip
2. Press the button on the impulse command block to kill all minecarts
3. Flick the lever next to the piston

Observed result:
After some time, the minecarts start floating and sticking next to each other.

Expected result:
The minecarts do not float mid-air.