I had a Plaguefall route, I've created a new route with the data of the old one, and wanted to adjust it, when I got the following lua error.
After this event the add pull button is gone. After a reload the add pull button is back, and I can see it created the new blank pull.

Message: Interface\AddOns\DungeonTools\DungeonEnemies.lua:917: attempt to index field '?' (a nil value) Time: Mon Feb 22 18:30:35 2021 Count: 1 Stack: Interface\AddOns\DungeonTools\DungeonEnemies.lua:917: attempt to index field '?' (a nil value) [string "@Interface\AddOns\DungeonTools\DungeonEnemies.lua"]:917: in function DungeonEnemies_GetPullColor'
[string "@interface\AddOns\DungeonTools\AceGUIWidget-DungeonToolsPullButton.lua"]:1158: in function SetIndex' [string "@Interface\AddOns\DungeonTools\DungeonTools.lua"]:4111: in function ReloadPullButtons'
[string "@interface\AddOns\DungeonTools\DungeonTools.lua"]:4155: in function `AddPull'
[string "@interface\AddOns\DungeonTools\AceGUIWidget-DungeonToolsNewPullButton.lua"]:27: in function <...geonTools\AceGUIWidget-DungeonToolsNewPullButton.lua:16>

Locals: self =

{
DeleteAllPresets = defined @interface\AddOns\DungeonTools\DungeonTools.lua:3192
DungeonEnemies_UpdateSelected = defined @interface\AddOns\DungeonTools\DungeonEnemies.lua:843
GetCurrentPull = defined @interface\AddOns\DungeonTools\DungeonTools.lua:2359
LiveSession_RequestSession = defined @interface\AddOns\DungeonTools\LiveSession.lua:83
PingMap = defined @interface\AddOns\DungeonTools\DungeonTools.lua:2333
AddPull = defined @interface\AddOns\DungeonTools\DungeonTools.lua:4153
DungeonEnemies_UpdateSeasonalAffix = defined @interface\AddOns\DungeonTools\DungeonEnemies.lua:950
HideInterface = defined @interface\AddOns\DungeonTools\DungeonTools.lua:693
GetBlip = defined @interface\AddOns\DungeonTools\DungeonEnemies.lua:759
RestoreScrollframeScripts = defined @interface\AddOns\DungeonTools\toolbar.lua:498
GetFullScreenSizes = defined @interface\AddOns\DungeonTools\DungeonTools.lua:879
ADDON_LOADED = defined @interface\AddOns\DungeonTools\DungeonTools.lua:144
UpdateDungeonEnemies = defined @interface\AddOns\DungeonTools\DungeonTools.lua:2636
IsFrameOffScreen = defined @interface\AddOns\DungeonTools\DungeonTools.lua:1021
dungeonEnemies = {
}
IsCurrentPresetTyrannical = defined @interface\AddOns\DungeonTools\DungeonTools.lua:2294
POI_CreateFramePools = defined @interface\AddOns\DungeonTools\Pointsofinterest.lua:9
CreateDevPanel = defined @interface\AddOns\DungeonTools\devpanel.lua:134
StartEraserDrawing = defined @interface\AddOns\DungeonTools\toolbar.lua:841
SetLivePreset = defined @interface\AddOns\DungeonTools\DungeonTools.lua:2429
GetDungeonName = defined @interface\AddOns\DungeonTools\DungeonTools.lua:259
LiveSession_SendPreset = defined @interface\AddOns\DungeonTools\LiveSession.lua:201
UpdateEnemyInfoData = defined @interface\AddOns\DungeonTools\EnemyInfo.lua:553
HardReset = defined @interface\AddOns\DungeonTools\DungeonTools.lua:5068
CleanEnemyData = defined @interface\AddOns\DungeonTools\DungeonEnemies.lua:1333
GetHighestFrameLevelAtCursor = defined @interface\AddOns\DungeonTools\toolbar.lua:529
DisplayBlipTooltip = defined @interface\AddOns\DungeonTools\DungeonEnemies.lua:460
ClearPull = defined @interface\AddOns\DungeonTools\DungeonTools.lua:4190
StringToTable = defined @interface\AddOns\DungeonTools\Transmission.lua:93
SkinProgressBar = defined @interface\AddOns\DungeonTools\DungeonTools.lua:994
MakeRenameFrame = defined @interface\AddOns\DungeonTools\DungeonTools.lua:4267
DungeonEnemies_UpdateBoralusFaction = defined @interface\AddOns\DungeonTools\DungeonEnemies.lua:996
initToolbar = defined @interface\AddOns\DungeonTools\toolbar.lua:14
POI_UpdateAll = defined @interface\AddOns\DungeonTools\Pointsofinterest.lua:486
OpenCustomColorsDialog = defined @interface\AddOns\DungeonTools\DungeonTools.l`