Data Export Widget Problems

Hi there
I'm trying to use the Data Export widget to get a .csv of some data but I get unexpected results dependings on said data
Sometimes I get a well-formed csv but sometimes I get a 2-lines file with the second one being JSON
And another time where it should behave the good way (pretty much the same type of DataShape) I get this error :
com.thingworx.types.primitives.StringPrimitive cannot be cast to com.thingworx.types.primitives.NumberPrimitive

Help please !