Results with Heroes ON, Scar ON, Annihilation on 2p_Deadman's Crossing using HARD AI:
Player0 = SM AI
Player1 = Tyranid AI
Pre-0.4 Tyranid Mod Release = No Fatal AI error whatsoever over multiple games
0.4 Tyranid Mod Release = Consistent Fatal AI error just around AI updates to Tier2 (first HQ addon)
Conclusion: I would say the Nid 0.4 release is corrupt somewhere so I would wait on making any fixes. Let the Nid team sort this out as I told them 1+ weeks ago about this so they are aware.
The Error again:
*ALERT: [string "Heroes/Core/heroes_manager.scar"]:359: attempt to index field `?' (a nil value) Could not execute rule: Hero_MainRule FATAL Scar Error while running rules - Execution has been paused.
Line in question:
if (g_aUnitList[g_iPlayer][iLoop1].Modifications["ModHealthMax"][1] == nil or