AttachmentTypes should be lowercase. 
https://github.com/EsotericSoftware/spine-runtimes/blob/master/spine-libgdx/src/com/esotericsoftware/spine/attachments/AttachmentType.java#L34
This is because they are lowercase in the JSON and this allows them to be looked up more easily. I'll merge the getAttachmentBySlotIndex fix. Thanks!