Hi @TH1,
It seems like this issue was introduced with the February release. A defect has been logged against this behavior (BUG-000156413).
In the meantime, you can work around this issue by manually adding "Elevation 3D Layer" to the "typeKeywords" in the JSON of the item using ArcGIS Online Assistant.
Please keep in mind that ArcGIS Online Assistant is not a supported product.
Best,
MJ