When a minecart is meant to bump into a full block to turn the other direction, it doesn't fully collide with the block, it has about 1/3 block space inbetween it and the block when it "bumps"

This is causing chunk unloading issues where the minecart will stop moving altogether if it happened to unload here.

Recreating:
Put a powered rail against a block so the cart will go back and forth
notice when the cart gets close to the block it preemptively bumps

Recreating the chunk unload:
Do the same thing only use a hopper minecart and fill it with a few things
create a cart unloader at one of the end points
when the cart is about to finish dropping off items unload the chunk
If caught at the right moment the cart will not resume movement when the rails get repowered.

Two images showing where the cart hits when it turns around one image with an unpowered rail and it aligns properly