With the latest snapshot, the sidebar display slot no longer changes, regardless of what objective you have assigned or are assigning to it.

This is somewhat a duplication of MC-31777 but since it has been marked as Fixed/Resolved and is in another snapshot, I have chosen to make a new issue.

Reproduce:

Use following command to make an objective:

/scoreboard objectives add Test dummy

Now, add it to the sidebar with following command:

/scoreboard objectives setdisplay sidebar Test

If you already have an objective on the sidebar (made in earlier versions) it will still update that objectives score, but you wont be able to change it to a new objective.