The bug

When teleporting a chest or hopper minecart between dimensions, the minecart drops its contents at its source point. It arrives at the destination entirely empty. This does not happen when the minecarts moves through a portal manually. Scoreboard scores are also lost, though the minecart's custom name and other data are maintained.

How to reproduce

1. Get a minecart with some items inside:

   /summon chest_minecart ~ ~ ~ {Items:[{id:"diamond",Count:1b}]}
   

2. (optional) Give it a score:

   /scoreboard objectives add test dummy
   /scoreboard players set @e[type=chest_minecart] test 5
   /scoreboard objectives setdisplay sidebar test
   

3. Teleport it to another dimension

   /execute in the_nether run tp @e[type=chest_minecart] 0 64 0
   

   → The item is left behind and the score is lost