Unfortunately this is quite common with Hoyas. A plant stressed from shipping or a plant allowed to dry out too much will often do this. Usually the new growth will only ever die back to the first mature leaves so it's upsetting but nothing to really worry about. Also if you are not already aware the new growth and growing tip should always be oriented upwards. Directing the growing tip down will often cause dieback.

Mike

Yeah I have to second Mike's assessment. I have had vines die back further than expected as they get their feet under them. All you can do is be attentive to its needs and it will turn things around when it has its feet under it. As long as it's not losing leaves, a little vine loss is not very worrisome, even though it's frustrating. Are these vines sharing the same roots or two separate cuttings?