>Looks like this might be known behaviour. See: https://stackoverflow.com/questions/31736496/why-does-adding-additional-angularjs-validation-directives-cause-asyncvalidator
>and https://github.com/angular/angular.js/issues/14691
>
>As suggested earlier there may be some condition that you can check in your directive to determine whether the asyncValidator actually needs to run. If it does not then you could just short-circuit the http call

Do you know what condition that may be? In the meantime I also asked on StackOverflow (I didn't see your message until now)

https://stackoverflow.com/questions/46101820/do-asyncvalidators-fire-all-the-time