Hi,
From the screenshots you provided, both the original terrain data from PVCase and the imported data in PVSyst appear to be quite similar and show regular flat lines, which indicates that the terrain is flat in both cases.
However, I understand that you perceive a difference in the terrain's appearance between PVCase and PVSyst. To help us better understand and diagnose the issue, could you please provide more details on the following points:
Are there any specific coordinates or points in the CSV file where you notice the discrepancy in the slope?
Could you share the CSV file with us so we can inspect it directly?