Repeating action sequence

So I made a new animation and skill for one of my monsters but every time they use it, the default action sequence for attack plays.
I don't have any action sequence notes for this skill.

Does anyone know what could cause this?

first, you need to tell us what plugins you're using - because there is no "default action sequence", simply because the default without plugins does not contain any action sequences at all.

as for the error - it could be a wrong setting in the plugin that handles the action sequence, an incompatibility with another plugin or simply plugins in the wrong order or so - so please add a screenshot of your plugin manager as well, so that we can check all that.