We identified and have a fix for the projection/conversion problem. It'll be included in the next release of ArcGIS Pro. Thank you for reporting it. My understanding of the issue is it should have been present in previous versions, not something we introduced at 1.4. Unfortunately for right now, the only work around I can provide is to project the data manually to WGS84 before running the Layer to KML tool. I'm sorry for the inconvenience this has caused you.
Can you explain what you mean by cannot use the tool with unique value symbology? What results are you getting in your output KML?
As for rolling back - no, there is no mechanism to roll back a version. You'd have to uninstall ArcGIS Pro 1.4 and re-install ArcGIS Pro 1.3.