How to reproduce:

1. /scoreboard objectives add healthbar dummy (the objective is a dummy cititeria, name just healthbar''

2. /scoreboard objectives setdisplay sidebar healthbar

3. /summon Skeleton ~ ~1 ~

{SkeletonType:1,UUID:11111111-1111-1111-1111-111111111111}

4. /scoreboard players set @e healthbar 40

5. /scoreboard players set @e healthbar 9

{Health_min:6s}

What should happen, is that the objective for that entity get updated to 9, but it will not do that.