In chat:
BigWigs: An invalid spell id (421) is being used in a boss module.

And a couple of lua errors:
379x BigWigs: One of your addons caused an error on the "BigWigs_SetInfoBoxBar" callback:
BigWigs_Plugins\InfoBox.lua:443: attempt to index local 'bar' (a nil value)
[string "@BigWigs_Core\BossPrototype.lua"]:1694: in function `SetInfoBar'
[string "@BigWigs_Legion\Antorus\CovenofShivarra.lua"]:465: in function <...ceBigWigs_Legion\Antorus\CovenofShivarra.lua:462>

Locals:
Skipped (In Encounter)

17x ...ceBigWigs_Legion\Antorus\CovenofShivarra.lua:185: bad argument #1 to 'format' (string expected, got nil)
[string "=[C]"]: in function format' [string "@BigWigs_Legion\Antorus\CovenofShivarra.lua"]:185: in function <...ceBigWigs_Legion\Antorus\CovenofShivarra.lua:175> [string "@BigWigs_Legion\Antorus\CovenofShivarra.lua"]:384: in function ?'
[string "@BigWigs_Core\BossPrototype.lua"]:523: in function <BigWigs_Core\BossPrototype.lua:489>

Locals:
Skipped (In Encounter)

Version 9.0.2