Summary:
When converting a world with a hopper minecart on a rail from CU49 (build 1.12 1622.0 6.1) they are converted without functionality. They simply don't pickup any item, until broken and replaced by a new hopper minecart.

Steps to reproduce:
Create a minecart track like the image below (in console edition).

Convert the world
Try for the hopper minecarts to pickup any items.
Result:
Hopper minecarts won't pick up any items until broken and replaced by a new one.
Video:
https://youtu.be/mLju-BrH4f0
World Receipt: