The Bug

Bossbar names that have scores won't update properly after exiting and re-entering the world.

How to Reproduce:

1. Input these 5 commands:

/scoreboard objectives add score dummy
/scoreboard players set player score 5
/scoreboard objectives setdisplay sidebar score
/bossbar add minecraft:boss ["",{"text":"Boss: "},{"score":{"name":"player","objective":"score"}}]
/bossbar set minecraft:boss players @a

You should see Boss: 5 at the top of your screen, and a score of 5 in the sidebar.

2. Input these 2 commands:

/scoreboard players add player score 5
/bossbar set minecraft:boss name ["",{"text":"Boss: "},{"score":{"name":"player","objective":"score"}}]

As intended, you should see Boss: 10 at the top of your screen, and a score of 10 in the sidebar.

3. Exit and re-open your world.

4. Repeat step 2. This time, you'll see Boss: 10 at the top of your screen, and a score of 15 in the sidebar.

No matter how much you try to update the name of the bossbar, you'll get the error feedback:

Nothing changed. That's already the name of this bossbar

That's a different result from what we got before.

You can give the bossbar different JSON and it'll update, but as long as the same JSON is being used, we can no longer update the score that appears in the bossbar name.