Lines do not position themselves correctly on the graph:
Hi @balupton, the reason why you are experiencing this issue is because Highcharts does not support 3D line charts. If you would like to combine scatter with lines, you will have to go with 2D as in this example: http://www.highcharts.com/demo/combo-regression
Scatter with positive lineWidth will work in 3D instead of line - https://jsfiddle.net/1zcne6Ln/2/
To better track how popular the enhancement idea is please use userVoice.
https://highcharts.uservoice.com/forums/55896-highcharts-javascript-api/suggestions/14921250-support-more-3d-chart-types
Closing the issue for now, but it could get reopened when implementation of the feature will be started.
Most helpful comment
Scatter with positive lineWidth will work in 3D instead of line - https://jsfiddle.net/1zcne6Ln/2/