Didn't do anything special, logged in and got the error when I opened the mailbox. The item is a drop from a Timewalking dungeon I didn't loot. I'm using the twitch release if that matters.

2x LastSeen\Main.lua:307: attempt to compare number with nil
[string "@lastseen\Main.lua"]:307: in function <LastSeen\Main.lua:72>

Locals:
self = {
0 =
}
event = "MAIL_INBOX_UPDATE"
mailItems = 1
(for index) = 1
(for limit) = 1
(for step) = 1
i = 1
_ = 960784
_ = 134327
sender = "The Postmaster"
subject = "Recovered Item"
(for index) = 1
(for limit) = 16
(for step) = 1
j = 1
(*temporary) = nil
(*temporary) = 2
(*temporary) = defined =[C]:-1
(*temporary) = "|cffffffff|Hitem:109879::::::::120:252:512:22:2:6424:6652:120:::|h[]|h|r"
(*temporary) = 960784
(*temporary) = "INVTYPE_WRIST"
(*temporary) = 960784
(*temporary) = 4
(*temporary) = 4
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = "attempt to compare number with nil"
addonTbl =

{
doNotIgnore = false
AddCreatureByNameplate = defined @lastseen\Handlers\NameplateHandler.lua:27
LoadSettings = defined @lastseen\Settings.lua:138
isAutoLootPlusLoaded = false
ignoredItemCategories = {
}
AddQuest = defined @lastseen\Handlers\QuestHandler.lua:12
New = defined @lastseen\Handlers\ItemHandler.lua:10
GetQuestInfo = defined @lastseen\Handlers\QuestHandler.lua:23
GetTable = defined @lastseen\Handlers\FunctionHandler.lua:280
questID = 0
maxHistoryEntries = 20
removedItems = {
}
Search = defined @lastseen\Handlers\FunctionHandler.lua:55
Contains = defined @lastseen\Handlers\FunctionHandler.lua:253
wasUpdated = false
itemSourceCreatureID = 0
ignoredItems = {
}
Update = defined @lastseen\Handlers\ItemHandler.lua:52
isFasterLootLoaded = false
Remove = defined @lastseen\Handlers\FunctionHandler.lua:23
query = ""
lootFast = false
L = {
}
GetCurrentMap = defined @lastseen\Handlers\FunctionHandler.lua:148
rarity = 2
OnTooltipSetItem = defined @lastseen\Handlers\FunctionHandler.lua:189
itemsToSource = {
}
AddCreatureByMouseover = defined @lastseen\Handlers\NameplateHandler.lua:6
mode = "Debug"
DataIsValid = defined @lastseen\Handlers\FunctionHandler.lua:168
RollHistory = defined @lastseen\Handlers\FunctionHandler.lua:289
GetTableKeyFromValue = defined @lastseen\Handlers\FunctionHandler.lua:243
GetItemInfo = defined @lastseen\Handlers\FunctionHandler.lua:301
isInInstance = false
currentMap = "Warspear"
events = {
}
ExtractItemLink = defined @lastseen\Handlers\FunctionHandler.lua:223
GetCount = defined @lastseen\Handlers\FunctionHandler.lua:6
isLastSeenLoaded = true
AddItem = defined @lastseen\Handlers\ItemHandler.lua:132
doNotUpdate = false
}
InitializeTable = defined @lastseen\Main.lua:37
playerName = "Brando"
L = {
DATE = "06/13/2020"
INFO_MSG_IGNORED_ITEM = "This item is automatically ignored."
CMD_LOOT = "loot"
ERROR_MSG_CANT_COMPLETE_REQUEST = "Can't complete request: "
ADDON_NAME_SETTINGS = "|cff00ccffLastSeen|r"
SEARCH_OPTION_I = "i"
AUCTION_HOUSE = "Auction House"
CMD_DISCORD = "discord"
CMD_HISTORY = "history"
ADDON_NAME = "|cff00ccffLastSeen|r: "
DEBUG_MODE = "Debug"
INFO_MSG_ITEM_ADDED = " successfully added."
AUCTION_WON_SUBJECT = "Auction won:"
SEARCH_OPTION_C = "c"
RELEASE = "[2.0] "
CMD_REMOVE_SHORT = "rm"
ERROR_MSG_BAD_REQUEST = "Bad request. Please try again."
LOOT_ITEM_SELF = "You receive loot: "
INFO_MSG_POSTMASTER = "The Postmaster"
QUIET_MODE_DESC = "No output!
"
CMD_REMOVE = "remove"
INFO_MSG_LOOT_ENABLED = "Loot Fast mode enabled."
NORMAL_MODE_DESC = "Shows new and updated items.
"
CMD_VIEW = "view"
QUIET_MODE = "Quiet"
IS_UNKNOWN = "Unknown"
CMD_IMPORT = "import"
ERROR_MSG_CANT_ADD = "Can't add specif