Ah, it was so close
But actually managed to fix it, it's a simple missing "STR" before TASOTHGUARD on line 5122 alienDeployments.rul
The last strange glitch I found was tasoths in tleth part 3 having thermal launchers / PWT with 0 ammo, but armed. If you unload those, the ammo is pwt disruptor (the gun itself, not the ammo for it) which is weird. Maybe it was happening in vanilla, but I can't remember. Also few of the tasoth guards were unarmed at all (not even grenades).
Anyway, mod done. Was quite a ride. 3411 total subs detected, finished on feb 2040.
Will try to compose some overall impressions later.
Thx for such an awesome mod @Nord