The boss bar text is tinted by the sidebar as if it was behind it but still renders in front of the sidebar text. This is inconsistent with other texts that are tinted such as the F3 which is tinted and rendered behind sidebar. This relates to MC-193515 and MC-187267.

In order to replicate:

1. Run /scoreboard objectives add abc dummy
2. Run /scoreboard objectives setdisplay sidebar abc
3. Run these player commands for large scoreboard text:
   /scoreboard players set abcdefghijklmnopqrstuvwxyz abc -2147483647
   /scoreboard players set abcdefghijklmnopqrstuvwxyz2 abc -2147483647
   /scoreboard players set abcdefghijklmnopqrstuvwxyz3 abc -2147483647
   /scoreboard players set abcdefghijklmnopqrstuvwxyz4 abc -2147483647
   /scoreboard players set abcdefghijklmnopqrstuvwxyz5 abc -2147483647
   /scoreboard players set abcdefghijklmnopqrstuvwxyz6 abc -2147483647
   /scoreboard players set abcdefghijklmnopqrstuvwxyz7 abc -2147483647
   /scoreboard players set abcdefghijklmnopqrstuvwxyz8 abc -2147483647
   /scoreboard players set abcdefghijklmnopqrstuvwxyz9 abc -2147483647
   /scoreboard players set abcdefghijklmnopqrstuvwxyz10 abc -2147483647
   /scoreboard players set abcdefghijklmnopqrstuvwxyz11 abc -2147483647
   /scoreboard players set abcdefghijklmnopqrstuvwxyz12 abc -2147483647
   /scoreboard players set abcdefghijklmnopqrstuvwxyz13 abc -2147483647
   /scoreboard players set abcdefghijklmnopqrstuvwxyz14 abc -2147483647
   /scoreboard players set abcdefghijklmnopqrstuvwxyz15 abc -2147483647
4. Create multiple boss bars by spawning multiple wither or using these commands:

Creating Boss Bars (Command Block Required):
/bossbar add long ["",

{"text":"ABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZ","bold":true,"underlined":true,"strikethrough":true}

]

/bossbar add long2 ["",

{"text":"ABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZ","bold":true,"underlined":true,"strikethrough":true}

]

/bossbar add long3 ["",

{"text":"ABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZ","bold":true,"underlined":true,"strikethrough":true}

]

/bossbar add long4 ["",

{"text":"ABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVXYZ","bold":true,"underlined":true,"strikethrough":true}

]

Display Boss Bars:
/bossbar set long players @p
/bossbar set long2 players @p
/bossbar set long3 players @p
/bossbar set long4 players @p