Conditions.IsAttackedAndCannotIgnore - in what cases does this bull return true, and in what fallse? I've noticed that it does not always return true when in combat, sometimes false.

Sometimes it returns true if you can ignore the mobs attacking you, for example if you're on mount with the correct options or you're supposed to ignore pulls while traveling or if Conditions.ForceIgnoreIsAttacked is activated. 

I recommend you just decompile the binaries and see for yourself. Even with the code being obfuscated, you can usually see these simple things.