Thank you very much for the reports and I am very sorry for the issue!
I made a quick elevation in Archicad 25 INT 5005 and export it to DWF (with color and shadow turned on), however I was unable to reproduce the issue. Could it be possible that you have enabled Texture fill in the Elevation settings?
If not, I suggest reaching out to the local support with the project plan and steps to reproduce, so that they can start the investigation from here.
Thank you very much!
Technical Support Engineer