The bug

In versions before 17w47a scoreboard objectives of the criteria type health used to display the value with heart icons in the player list. Since 17w47a this is not the case anymore.

This is likely related to the fact that the render type is not written to the scoreboard.dat file, see this reddit comment.

How to reproduce

1. Use the following commands

   /scoreboard objectives add health health
   /scoreboard objectives setdisplay list health
   

2. Take damage, see MC-111729