FYI for Esri and anyone else that may run into this error.
Databases: Sql Server 2012 and Oracle 18.104.22.168
Exporting to runtime content in ArcGIS Desktop 10.3.0.4284 succeeds with one single point feature layer, but when loading the created .geodatabase file into ArcGIS runtime 10.2.4 results in the error "Non-convertible value type in convert" at the following line.
Geodatabase database2 = (await Esri.ArcGISRuntime.Data.Geodatabase.OpenAsync(DatabasePath));
Steps that reproduce:
1) Add a point feature layer in ArcMap
2) Open the layer properties for it
3) Select the display tab
4) In the Display Expression section for the Field selection choose "Object ID".
5) Share As -> ArcGIS Runtime Content
The analyze does not flag anything as wrong with either error or warning, but as stated the geodatabase won't load in the runtime. It may be reproducible with other feature class types / tables but I haven't tested them.