Describe the problem

What steps will reproduce the problem?

1. Noticed it started happening at phase two
2. Happened in LFR
3. Had same errors on few characters already

Consider attaching a screenshot below to help describe your issue (Attach directly, do not link to other websites)

What version of BigWigs are you using? (Stating 'latest' is not useful)

v252

Do you have an error log of what happened?

Yes:

1x ...s/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua:581: attempt to index upvalue 'stageOneTimers' (a nil value)
[string "@Interface/AddOns/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua"]:581: in function `?'
[string "@Interface/AddOns/BigWigs_Core/BossPrototype.lua"]:559: in function <Interface/AddOns/BigWigs_Core/BossPrototype.lua:525>

Locals:
Skipped (In Encounter)

1x ...s/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua:624: attempt to index upvalue 'stageOneTimers' (a nil value)
[string "@Interface/AddOns/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua"]:624: in function `?'
[string "@Interface/AddOns/BigWigs_Core/Core.lua"]:59: in function <Interface/AddOns/BigWigs_Core/Core.lua:54>

Locals:
Skipped (In Encounter)

1x ...s/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua:727: attempt to index upvalue 'stageOneTimers' (a nil value)
[string "@Interface/AddOns/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua"]:727: in function `?'
[string "@Interface/AddOns/BigWigs_Core/BossPrototype.lua"]:559: in function <Interface/AddOns/BigWigs_Core/BossPrototype.lua:525>

Locals:
Skipped (In Encounter)

1x ...s/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua:1095: attempt to index upvalue 'stageThreeTimers' (a nil value)
[string "@Interface/AddOns/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua"]:1095: in function `?'
[string "@Interface/AddOns/BigWigs_Core/BossPrototype.lua"]:559: in function <Interface/AddOns/BigWigs_Core/BossPrototype.lua:525>

Locals:
Skipped (In Encounter)

3x ...s/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua:631: attempt to index upvalue 'stageThreeTimers' (a nil value)
[string "@Interface/AddOns/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua"]:631: in function `?'
[string "@Interface/AddOns/BigWigs_Core/Core.lua"]:59: in function <Interface/AddOns/BigWigs_Core/Core.lua:54>

Locals:
Skipped (In Encounter)

2x ...s/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua:1165: attempt to index upvalue 'stageThreeTimers' (a nil value)
[string "@Interface/AddOns/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua"]:1165: in function `?'
[string "@Interface/AddOns/BigWigs_Core/BossPrototype.lua"]:559: in function <Interface/AddOns/BigWigs_Core/BossPrototype.lua:525>

Locals:
Skipped (In Encounter)

8x ...s/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua:1141: attempt to index upvalue 'stageThreeTimers' (a nil value)
[string "@Interface/AddOns/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua"]:1141: in function `?'
[string "@Interface/AddOns/BigWigs_Core/BossPrototype.lua"]:559: in function <Interface/AddOns/BigWigs_Core/BossPrototype.lua:525>

Locals:
Skipped (In Encounter)

3x ...s/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua:1123: attempt to index upvalue 'stageThreeTimers' (a nil value)
[string "@Interface/AddOns/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua"]:1123: in function `?'
[string "@Interface/AddOns/BigWigs_Core/BossPrototype.lua"]:559: in function <Interface/AddOns/BigWigs_Core/BossPrototype.lua:525>

Locals:
Skipped (In Encounter)

3x ...s/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua:675: attempt to index upvalue 'stageThreeTimers' (a nil value)
[string "@Interface/AddOns/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua"]:675: in function `?'
[string "@Interface/AddOns/BigWigs_Core/BossPrototype.lua"]:559: in function <Interface/AddOns/BigWigs_Core/BossPrototype.lua:525>

Locals:
Skipped (In Encounter)

3x ...s/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua:1158: attempt to index upvalue 'stageThreeTimers' (a nil value)
[string "@Interface/AddOns/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua"]:1158: in function `?'
[string "@Interface/AddOns/BigWigs_Core/BossPrototype.lua"]:559: in function <Interface/AddOns/BigWigs_Core/BossPrototype.lua:525>

Locals:
Skipped (In Encounter)

3x ...s/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua:1108: attempt to index upvalue 'stageThreeTimers' (a nil value)
[string "@Interface/AddOns/BigWigs_SanctumOfDomination/SylvanasWindrunner.lua"]:1108: in function `?'
[string "@Interface/AddOns/BigWigs_Core/BossPrototype.lua"]:559: in function <Interface/AddOns/BigWigs_Core/BossPrototype.lua:525>

Locals:
Skipped (In Encounter)

Any additional information? (example: WoW language if not English)

Do you have advanced combat logging enabled?

If you're talking about CVAR setting in the game, then the answer is no, I do not have it enabled. The above errors only occur during Sylvanas fight for me.

Looks like you were reloading UI mid combat?

I was trying to get rid of that error. I will test it again tomorrrow.