The bug
If multiple bossbars are active, the notch opacity of the second bossbar and below is messed up.
MC-146070
Bossbar notch opacity messed up when more than one bossbar is active
Resolved
Fixed
4
Piyotato
migrated
Confirmed
(Unassigned)
Minecraft 19w11b
Minecraft 19w13b
Retrieved
Can confirm. I was setting up notched boss bars to make a meme but the one below it was messing up so I used a progressive boss bar instead. I don't have a screenshot of the notched versions, but mine behaved exactly how yours did.