GRevit to Revit 2018 'outside design limits'

We have a definition that we are using to get rhino stadium terraced seating setting out linework into Revit so we can use Dynamo to populate the seating families.
This worked fine for Rhino5 to Revit2017. Rhino6 took a bit of tweaking to get the lists to work but works fine. Exporting to Revit2018 causes the issue:

‘Revitline Error
The input point lies outside of Revit design limits.
Parameter name:origin’

No geometry is loaded.
The same definition works fine with Revit2017.
Does anyone know what changed?

Based on the fact that “points” seems to be the problem; did float become double in the R6 version? Or perhaps a model origin problem?

// Rolf