I inflicted Doubt over 20 times in a battle and it only counted it as 2 times! Over all the rounds I was inflicting doubt on the entire team multiple times. This happened in 2 battles now! I counted...
Ideas
Assuming you are using Malgus for it. Only his slam will inflict doubt (so 1 count). The doubt from his unique is coded as self inflicted, so we don't get credit.
Dr Aphra is the easiest, she can apply doubt to all enemies (assuming they don't dodge or resist).
If you don't have Dr A, you should be able to speed it up with Cassian and have him spread it.
I don't have Aphra yet. I need to look into how Cassian would work for that.