Have been getting this every time I log in on, I believe, all of my characters.

Date: 2017-11-18 22:18:59
ID: 1
Error occured in: Global
Count: 1
Message: ...Tracker\Libs\LibPetJournal-2.0\LibPetJournal-2.0.lua line 101:
ClearFilters() already called
Debug:
[C]: ?
...Tracker\Libs\LibPetJournal-2.0\LibPetJournal-2.0.lua:101: ClearFilters()
...Tracker\Libs\LibPetJournal-2.0\LibPetJournal-2.0.lua:197: RestoreFilters()
...Tracker\Libs\LibPetJournal-2.0\LibPetJournal-2.0.lua:377: _LoadPetsFinish()
...Tracker\Libs\LibPetJournal-2.0\LibPetJournal-2.0.lua:310: LoadPets()
...Tracker\Libs\LibPetJournal-2.0\LibPetJournal-2.0.lua:423: ?()
...Tracker\Libs\LibPetJournal-2.0\LibPetJournal-2.0.lua:47:
...Tracker\Libs\LibPetJournal-2.0\LibPetJournal-2.0.lua:46
Locals:
(*temporary) = false
(*temporary) = "ClearFilters() already called"

AddOns:
Beautycase, v
Colorz, v
Swatter, v7.3.1 (<%codename%>)
WowheadLooter, v70300
AdvancedInterfaceOptions, v1.2.2
Altoholic, vr183
AngryWorldQuests, v
Auctionator, v4.0.19
Babylonian, v5.1.DEV.332(/embedded)
BattlePetDailyTamer, v2.1.7
BattlePetBreedID, vr162
BonusRollPreview, v@project-version@
cargBagsNivaya, v
Configator, v5.1.DEV.431(/embedded)
DataStore, vr64
DataStoreAchievements, vr46
DataStoreAgenda, vr26
DataStoreAuctions, vr49
DataStoreCharacters, vr41
DataStoreContainers, vr57
DataStoreCrafts, vr78
DataStoreCurrencies, vr36
DataStoreGarrisons, vr22
DataStoreInventory, vr51
DataStoreMails, vr50
DataStorePets, vr43
DataStoreQuests, vr43
DataStoreReputations, vr41
DataStoreSpells, vr31
DataStoreStats, vr30
DataStoreTalents, vr60
DBMCore, v7.3.7
DBMDefaultSkin, v
DBMStatusBarTimers, v
DejaCharacterStats, v725r100
eAlignUpdated, v7.2.0
evlRaidStatus, v
ezFishing, v@project-version@
Gatherer, v7.3.1
GatherMate2, v1.41
GTFO, v4.43.6
HandyNotes, vv1.4.15
HandyNotesArgus, vv0.04
HandyNotesBrokenShore, vv1.21
HandyNotesHallowsEnd, vv1.2.7
HandyNotesHigherDimensionalLearning, v1
HandyNotesLegionClassOrderHalls, vv1.25
HandyNotesLegionTreasures, v1
HandyNotesSuramarShalAranTelemancy, vv1.11
LibProcessable, v21
lsToasts, v70300.03
Mapster, v1.7.6
MasterPlanA, vA
MaxCam, vv2.1.3
Molinari, v@project-version@
nBuff, v
nChat, v
ncHoverBind, v1.4.2
nCore, v
nMainbar, v
nMinimap, v
nPlates, v2.4
nTooltip, v
oUF, v@project-version@
oUFNeav, v
oUFNeavRaid, v
PetTracker, v7.3.0
PetTrackerBreeds, v7.3.0
PetTrackerConfig, v7.3.0
PetTrackerSwitcher, v7.3.0
PetTrackerUpgrades, v7.3.0
Postal, vv3.5.8
QuickQuest, v70200.30-Release
Rematch, v4.7.6
Skada, v1.7.2
skrFishStats, v0.2
skrItemScore, v
StopResetingMyCameraPlease, v
TomTom, vv70200-1.0.0-6d2e98b
Wasabi, v4
BlizRuntimeLib_enUS v7.3.2.70300
(ck=7b9)

I ended up fixing this just now. In case it helps anyone else... I believe that I had simply over-ridden the previous version when I last updated the addon. I deleted the PetTracker folders from the WoW AddOns folder and also removed the PetTracker files from SavedVariables and then re-installed it and it's good now.