Steps to reproduce

(full repro in new world shown here: https://youtu.be/BvWQy3EfSRc)

1. Create a new world, creative mode, coordinates on.
2. Make a small East-West rail track near spawn out of powered and normal rails. The track should have powered rails next to solid block at each end, one or more normal rails connect to those powered rails, and then a section of powered rails in the middle. I.e. a sequence such as [block, p-rail, rail, 3x p-rail, rail, p-rail, block]. Activate each section of powered rails with redstone in some way.
3. Place a hopper minecart on the rails and nudge it. Confirm that it moves back and forth along the whole length of the track.
4. Fly 200 blocks to the east, place a bed, and use it to set your spawn point.
5. Fly another about another 500 blocks east (possibly the threshold is 2x render distance from the rails).
6. Set gamemode to survival, then run /kill @s.
7. Respawn at your bed, then set gamemode back to creative for convenience.
8. Fly back to the rails and minecart.

Expected result

The minecart continues to move back and forth along the whole length of the track.

Observed result

The minecart stops at a certain point. It will not go past that point even if you push it and break the rails and blocks around that point. New minecarts placed on the track stop at that point as well. The space that stops minecarts seems to be the size of a minecart collision box--see this comment.

My minecarts suddenly began stopping on a single block today. The rail is within a single chunk (does not cross chunk boundary) and is repeatable with me in the chunk watching it happen (IE - I do not log out or leave the chunk in order to trigger the effect of the minecart stopping). The rail is a powered rail, however I tested this with both powered and regular rail and had the same issue. The cart arrives at the affected block and stops as if it was inside a full block (even though was a regular rail block). Further - I tested riding the minecart and attempting to push forward (up arrow) to get past the affected block and the minecart would not move. I appear to have several blocks affected by this issue within the same chunk. At first I thought this effect was because the rails were underwater, however I drained the area and recreated the problem without the water (IE on dry rail). The attached screenshot shows the cart on the rail on the affected block.