[MC-99259] As of 1.9, the wither health bar doesn't go up during spawn

The bug

When spawned with skulls and soul sand, the wither used to show its bar slowly filling up the health right before it was about to explode and be ready for fight. That is no longer the case in this version. Compare it with 1.8.9 to see the difference. This means also that command blocks are unable to detect the health of the wither.

Code analysis

Code analysis by @unknown can be found in this comment.

Linked issues

is duplicated by 3

MC-155339 Wither is broken (2 Bugs) Resolved

MC-164226 The Wither boss bar doesn't slowly fill up when you summon it. Resolved

MC-201041 Wither's bossbar not updating when in invulnerable state Resolved

Comments 20

[Mod] Asteraoth 2016-04-14T03:54:21Z

Confirmed for 16w15a and 16w15b

[Mod] Asteraoth 2016-05-02T00:14:40Z

Confirm for 1.9.3 pre-2

[Mod] Asteraoth 2016-05-15T07:11:15Z

Confirmed for 1.9.4

[Mod] Asteraoth 2016-05-21T22:43:45Z

Confirmed for 16w20a

[Mod] Asteraoth 2017-04-02T21:31:12Z

Confirmed for 17w13b

10 more comments

[Mod] Asteraoth 2018-07-18T18:57:41Z

Confirmed for 1.13

[Mod] Asteraoth 2018-08-01T17:58:17Z

Confirmed for 18w31a

W_V 2020-04-06T09:01:51Z

Confirmed for 20w14a

user-a4a49 2020-06-03T07:27:27Z

Confirmed in 20w22a.

jmp 2020-08-21T16:39:59Z

Can confirm that yes, this does still happen in 1.16.2. The fix mentioned by Insane96MCP works perfectly (moving the call to update the boss bar outside the if/else block). I recently fixed this bug in Paper with the following patch file (2 line diff): https://github.com/PaperMC/Paper/commit/c8542f236568b6e168f59d79b02d62d3fb11f690