[Mobhack]

AI player does not always buy field defence points, its a random choice to buy a batch as it loops through the purchase code many tmes over. A chance which can result in a "nope" for the choice - thus perhaps wasting any points the attacker has invested in breaching kit and engineers.

So, sometimes none may be bought, sometimes quite a lot and usually at least some. It's that random number thing again.

Same as it doesent always buy planes even if it has flights allocated to it, thus wasting any player points spent on AAA in anticipation of enemy air. Nor does it always buy off-map batteries (may buy a heavy mortar platoon or rocket troops instead).

The AI purchase code is complicated and based on many factors (e.g. it may like SS troosps for a given battle date versus a particular opponent, e.g. Canadians in Normandy)

So not a "bug" - but a feature. You just saw one of the times that after many passes through the buy loop, it has said "no thanks" to all mine buy choices.