If you use TR_Factions.esp it will overwrite and fix the issue.
Surprisingly the error is indeed in TR_Mainland.esm and not in TR_Factions.esp. Does this need a hotfix?

Other small issues found with TR_Factions:
Unlike what was in the release notes, not only Fighters, Mages and Telvanni have increased rank reputation requirements, but Thieves, Cult and Temple too, though more slightly,
The East Empire Company is edited only to add a 1 modifier to T_Glb_ArchaeologicalSociety. There's no call for that at this time since it isn't joinable by the player