See if you can reproduce the issue by re-importing the default head without changes.
Also, to my knowledge, there are no blend shapes in use in BDO, it's all bone morphs or animations, even for the face,
Nicknero
made a head mod for tamer, although he has done it through armor and used parthidedesc to hide the original head, he did mention that facial customization worked fine (which he believed wouldn't because he also assumed blend shapes were used), I'm not sure about facial expressions, but I see no reason why they wouldn't work.