It seems as if there's some new conflict with BigDebuffs and AtlasLootClassic. All was working well prior to the pre-patch update. As stated in the title, I do not notice any problems with the functionality of the addon. I simply get this error every time the UI loads.

Date: 2021-05-20 16:23:34
ID: 1
Error occured in: Global
Count: 1
Message: ..\AddOns\Questie\Questie.lua line 248:
attempt to concatenate local 'str' (a nil value)
Debug:
[string "@Questie\Questie.lua"]:248: Colorize()
[string "@Questie\Modules\QuestieMenu.lua"]:94:
Questie\Modules\QuestieMenu.lua:87
[string "@..\SharedXML\C_TimerAugment.lua"]:16:
..\SharedXML\C_TimerAugment.lua:14
Locals:
self =

{
SetDefaultModuleLibraries = defined @interface\AddOns\BigDebuffs\Libs\AceAddon-3.0\AceAddon-3.0.lua:367
Colorize = defined @interface\AddOns\Questie\Questie.lua:221
Enable = defined @interface\AddOns\BigDebuffs\Libs\AceAddon-3.0\AceAddon-3.0.lua:294
RegisterChatCommand = defined @interface\AddOns\Questie\Libs\AceConsole-3.0\AceConsole-3.0.lua:85
GetClassColor = defined @interface\AddOns\Questie\Questie.lua:251
EnableModule = defined @interface\AddOns\BigDebuffs\Libs\AceAddon-3.0\AceAddon-3.0.lua:332
modules = {
}
GetModule = defined @interface\AddOns\BigDebuffs\Libs\AceAddon-3.0\AceAddon-3.0.lua:210
IterateEmbeds = defined @interface\AddOns\BigDebuffs\Libs\AceAddon-3.0\AceAddon-3.0.lua:442
started = true
UnregisterComm = defined @interface\AddOns\AtlasLootClassic\Libs\CallbackHandler-1.0\CallbackHandler-1.0.lua:153
defaultModuleLibraries = {
}
TimeLeft = defined @interface\AddOns\Questie\Libs\AceTimer-3.0\AceTimer-3.0.lua:172
Deserialize = defined @interface\AddOns\NovaWorldBuffs\Lib\AceSerializer-3.0\AceSerializer-3.0.lua:246
UnregisterChatCommand = defined @interface\AddOns\Questie\Libs\AceConsole-3.0\AceConsole-3.0.lua:111
minimapConfigIcon = {
}
ScheduleRepeatingTimer = defined @interface\AddOns\Questie\Libs\AceTimer-3.0\AceTimer-3.0.lua:129
CancelAllTimers = defined @interface\AddOns\Questie\Libs\AceTimer-3.0\AceTimer-3.0.lua:160
Printf = defined @interface\AddOns\Questie\Libs\AceConsole-3.0\AceConsole-3.0.lua:69
RegisterBucketEvent = defined @interface\AddOns\Questie\Libs\AceBucket-3.0\AceBucket-3.0.lua:184
SetDefaultModulePrototype = defined @interface\AddOns\BigDebuffs\Libs\AceAddon-3.0\AceAddon-3.0.lua:409
TBC_BETA_BUILD_VERSION_SHORTHAND = ""
baseName = "Questie"
Debug = defined @interface\AddOns\Questie\Questie.lua:281
name = "Questie"
Error = defined @interface\AddOns\Questie\Questie.lua:277
IsEnabled = defined @interface\AddOns\BigDebuffs\Libs\AceAddon-3.0\AceAddon-3.0.lua:451
orderedModules = {
}
ScheduleTimer = defined @interface\AddOns\Questie\Libs\AceTimer-3.0\AceTimer-3.0.lua:94
DisableModule = defined @interface\AddOns\BigDebuffs\Libs\AceAddon-3.0\AceAddon-3.0.lua:350
HandleSlash = defined @interface\AddOns\Questie\Questie.lua:217
OnDisable = defined @interface\AddOns\Questie\Questie.lua:213
OnEnable = defined @interface\AddOns\Questie\Questie.lua:209
OnUpdate = defined @interface\AddOns\Questie\Questie.lua:205
RegisterMessage = defined @interface\AddOns\AtlasLootClassic\Libs\CallbackHandler-1.0\CallbackHandler-1.0.lua:90
GetArgs = defined @interface\AddOns\Questie\Libs\AceConsole-3.0\AceConsole-3.0.lua:144
Print = defined @interface\AddOns\Questie\Libs\AceConsole-3.0\AceConsole-3.0.lua:54
OnInitialize = defined @interface\AddOns\Questie\Questie.lua:134
UnregisterAllBuckets = defined @interface\AddOns\Questie\Libs\AceBucket-3.0\AceBucket-3.0.lua:229
UnregisterBucket = defined @interface\AddOns\Questie\Libs\AceBucket-3.0\AceBucket-3.0.lua:206
RegisterBucketMessage = defined @interface\AddOns\Questie\Libs\AceBucket-3.0\AceBucket-3.0.lua:200
IsModule = defined @interface\AddOns\BigDebuffs\Libs\AceAddon-3.0\AceAddon-3.0.lua:468
db = {
}
SetDefaultModuleState = defined @interface\AddOns\BigDebuffs\Libs\AceAddon-3.0\AceAddon-3.0.lua:387
SendCommMessage = defined @interface\AddOns\NovaWorldBuffs\Lib\AceComm-3.0\AceComm-3.0.lua:87
UnregisterAllComm = defined @interface\AddOns\AtlasLootClassic\Libs\CallbackHandler-1.0\CallbackHandler-1.0.lua:174
SetEnabledState = defined @interface\AddOns\BigDebuffs\Libs\AceAddon-3.0\AceAddon-3.0.lua:424
Serialize = defined @interface\AddOns\NovaWo
AddOns:
MoncaiCompare, v7.2.0
Swatter, v1.13.6652 (SwimmingSeadragon)
AtlasLootClassic, vv2.1.0
AtlasLootClassicData, vv2.1.0
AtlasLootClassicDungeonsAndRaids, vv2.1.0
AtlasLootClassicMaps, vv1.0.0
Bagnon, v9.0.6
BigDebuffs, vv10.0
ClassicInterrupt, v
DisenchantCraftedItems, v2.0.1
GuildRosterManager, v1.928
Informant, v1.13.6650 (SwimmingSeadragon)
LootMagic, v1.0
MooidesMountMod, v1.0
NovaWorldBuffs, v2.02
OmniBar, vv11.5
OmniCC, v9.0.10
Postal, vr436
Questie, v6.3.11
SigmaProfessionFilter, v
SigmaProfessionFilterEnchanting, v
Stubby, v1.13.6614 (SwimmingSeadragon)
ToLevel, v0.1
WeakAuras, v3.4.1
WeakAurasCompanion, v1.1.0
ZygorGuidesViewerClassicTBC, v7.0
BlizRuntimeLib_enUS v2.5.1.20501
(ck=2f1)

We reworked the init process of Questie a few updates back which should have fixed issues like this.

If you still experience this, feel free to open up a new issue.