I have a vsd file that I resave as vsdx and some of the texts change their font. Not all, just a few textboxes.
For example if I resave the original.vsd in files.zip (265.1 KB) I get original resaved.vsdx. If you look at the formatting of the text “Qualifikationen/Schulungen”, you will see that it has Arial font in the vsd while Calibri in the vsdx.
We were able to replicate the issue in our environment while using Aspose.Diagram for .NET 18.9 and logged it as DIAGRAMNET-51521 in our issue tracking system. We will further look into details of the issue and keep you posted with the status of its correction. Please be patient and spare us little time.
We would like to share with you that your issue has been resolved in hotfix version Aspose.Diagram for .NET 18.9.1. You may please download hotfix from given link and in case you face any issue, please feel free to let us know.