Schall Tank Platoon crashes with "attempt to index field '?' ( a nil value) on line 1 of ammo.lua:
data.raw["ammo"]["flamethrower-ammo"].ammo_type[2].consumption_modifier = 1; --1.125
if loading with aai's various vehicle mods. It did not reference AAI in the crash, only STP, though.

Specifically: crashes if loaded with either of the following aai vehicles: [flame tank, flame tumbler]
However aai vehicles: chaingunner, hauler, laser tank, miner, and warden will load along with STP without crashing.

combinations tested: large modpack>100 mods, all aai mods+STP, vanilla+STP+other military mods excluding aai, individual aai mods with STP. Traced to only two: flame tank and/or flame tumbler.

add: if data.raw["ammo"]["flamethrower-ammo"] and data.raw["ammo"]["flamethrower-ammo"].ammo_type[2] then
to top of ammo.lua
and terminate after first config-dependent paragraph that sets:
data.raw["ammo"]["flamethrower-ammo"].ammo_type[2].action.action_delivery.stream = "handheld-flamethrower-fire-stream";

that makes it possible for either of the aai mods to load with STP, though not sure if that causes issues elsewhere

Fixed in 0.16.3, you should be able to use both mods now.
The cause is AAI Flame Tank mod replaced the vanilla flamethrower ammo with its own. It's likely that AAI Flame Tank mod may conflict with any other mods which deals with flamethrower ammo.