I did not see any other bug reports for this.

Confirmed on Windows 10 and Xbox One Bedrock.

Happening on a multiplayer/online realm, unable to use commands or host privileges on this world.

A minecart on a continuous movement loop will bug, either freezing, disappearing, or falling off the tracks.  Loading and unloading the chunk or area might be the situation when the minecart loses it's continuous movement.

Recreate:

  Place a line (10-12) of powered redstone rails and regular rails with inclines at each end.

  Place a block at the top of each incline so the rail cart will hit the block and reverse once it hits the top of the incline, propelling it into a continuous "pendulum" of motion.

  Place a hopper-minecart on the rail

  Push the minecart so it starts in motion moving infinitely back and forth on the rails/redstone rails.

  Fly out of the chunk or area so this is unloaded - then fly back into the area after some time and load the chunk again

  On occasions, reloading the chunk/area the minecart will either have disappeared, be frozen on the tracks, or have fallen off the rail!

Expected results:

  Hopper-minecarts should be able to move continuously on a redstone-powered/momentum loop.

  Hopper-minecarts should not freeze, disappear, or somehow teleport off the rails randomly!

  Loading and unloading chunks/areas should not cause hopper-minecarts to freeze, disappear, or somehow teleport off the rails

  Lag should not cause hopper-minecarts to freeze, disappear, or somehow teleport off the rails

  Some crazy bug in the game shouldn't exist, causing hopper-minecarts to freeze, disappear, or somehow teleport off the rails!

This can be hard to recreate because #1 it's happening on an online world/realm, #2 it happens at random, #3 we don't know the exact source causing the bug.

We guess it is either lag or chunk loading that makes the minecarts bug out!