I believe to have found an error in the export_descr_character_traits of the Roman expansion. The trigger for the emperor title:
Trigger Promote_to_Imperator
WhenToTest CharacterTurnEnd
Condition FactionType romans_brutii
and IsFactionLeader
and Trait HouseCaesar = 1
and Trait Dictator = 0
and not Trait Imperator > 0
and I_SettlementOwner Rome = romans_brutii
Affects Imperator 2 Chance 100 <--this line gives the Roman faction leader the second level of the Imperator trait, but as you can see below, there is only one level:
Trait Imperator
Characters family
ExcludeCultures barbarian, greek, eastern, egyptian, carthaginian, nomad
AntiTraits Dictator, Caesar, Senator
Level Imperator
Description Imperator_desc
EffectsDescription Imperator_effects_desc
GainMessage Imperator_gain_desc
Epithet Imperator_epithet_desc
Threshold 1
Effect Influence 5