[1.8->1.7] Custom boss bars do not display correctly

[calcastor]

/viaversion dump Output

https://dump.viaversion.com/be943bbbf6ed10f6f1aae5f1712118f56d8397c43127f39e01456ec6790fde61

Console Error

N/A

Bug Description

Custom bossbars created with Adventure display only as "Wither" for 1.7.10 clients connected to 1.8.8 servers.

Steps to Reproduce

1. Log on to a 1.8.8 server with 1.7.10
2. Do something to make a custom boss bar (the bug report case implements them with Adventure)
3. Observe only the "Wither" mob title and no custom progress or otherwise in the boss bar

Expected Behavior

The boss bar should represent what it does in 1.8.8

Additional Server Info

No response

Checklist

• [X] Via plugins are only running on EITHER the backend servers (e.g. Paper) OR the proxy (e.g. BungeeCord), not on both.
• [X] I have included a ViaVersion dump.
• [X] If applicable, I have included a paste (not a screenshot) of the error.
• [X] I have tried the latest build(s) from https://ci.viaversion.com/ and the issue still persists.
• [X] I have looked at https://www.spigotmc.org/resources/viarewind-legacy-support.52924/ and it does not offer a fix for my problem

[Barvalg]

[FlorianMichael]

Is this something which started happening with the current release or can you also reproduce it on this builds: ViaVersion: https://github.com/ViaVersion/ViaVersion/releases/tag/4.9.3 ViaBackwards: https://hangar.papermc.io/ViaVersion/ViaBackwards/versions/4.9.2 ViaRewind: https://hangar.papermc.io/ViaVersion/ViaRewind/versions/3.0.6

[calcastor]

Is this something which started happening with the current release or can you also reproduce it on this builds: ViaVersion: https://github.com/ViaVersion/ViaVersion/releases/tag/4.9.3 ViaBackwards: https://hangar.papermc.io/ViaVersion/ViaBackwards/versions/4.9.2 ViaRewind: https://hangar.papermc.io/ViaVersion/ViaRewind/versions/3.0.6

This issue does not occur on these builds.

[FlorianMichael]

Are you sure this is a 1.8 server or is it 1.9+?

[calcastor]

Are you sure this is a 1.8 server or is it 1.9+?

It is a 1.8.8 Paper fork called SportPaper however this is a custom build with some separate changes.

[FlorianMichael]

Yeah I found the issue already, was confused at the beginning.