Starting on a 1.16.4 world, when those scoreboards are created : 

/scoreboard objectives add time minecraft.custom:minecraft.play_one_minute
/scoreboard objectives add grass minecraft.broken:minecraft.grass_path
/scoreboard objectives list

The game confirm that those 2 objectives exist.

Now when opening the world in 1.17-pre4, and doing this again:

/scoreboard objectives list

 
The 2 scoreboard were removed.
This is probably caused by the fact that those objective name changed "play_one_minute" -> "play_time" and "grass_path" -> "dirt_path", but there is 2 distinct datafixer supposed to handle that.