Core/Auras: Only auras that are stackable to use the same slot

src/server/game/Entities/Unit/Unit.cpp

@@ -3149,7 +3149,7 @@ Aura* Unit::_TryStackingOrRefreshingExistingAura(SpellInfo const* newAura, uint8
     ASSERT(casterGUID || caster);
 
     // Check if these can stack anyway
-    if (!casterGUID && (newAura->IsChanneled() || newAura->AttributesEx3 & SPELL_ATTR3_STACK_FOR_DIFF_CASTERS))
+    if (!casterGUID && !newAura->IsStackableOnOneSlotWithDifferentCasters())
         casterGUID = caster->GetGUID();
 
     // passive and Incanter's Absorption and auras with different type can stack with themselves any number of times

src/server/game/Spells/SpellInfo.cpp

@@ -1030,6 +1030,12 @@ bool SpellInfo::IsMultiSlotAura() const
     return IsPassive() || Id == 55849 || Id == 40075 || Id == 44413; // Power Spark, Fel Flak Fire, Incanter's Absorption
 }
 
+bool SpellInfo::IsStackableOnOneSlotWithDifferentCasters() const
+{
+    /// TODO: Re-verify meaning of SPELL_ATTR3_STACK_FOR_DIFF_CASTERS and update conditions here
+    return StackAmount > 1 && !IsChanneled() && !(AttributesEx3 & SPELL_ATTR3_STACK_FOR_DIFF_CASTERS);
+}
+
 bool SpellInfo::IsDeathPersistent() const
 {
     return AttributesEx3 & SPELL_ATTR3_DEATH_PERSISTENT;

src/server/game/Spells/SpellInfo.h

@@ -392,6 +392,7 @@ public:
     bool IsStackableWithRanks() const;
     bool IsPassiveStackableWithRanks() const;
     bool IsMultiSlotAura() const;
+    bool IsStackableOnOneSlotWithDifferentCasters() const;
     bool IsDeathPersistent() const;
     bool IsRequiringDeadTarget() const;
     bool IsAllowingDeadTarget() const;