In Infrastructure Studio, when you select fonts to be used for labeling or text layers, the fonts listed are those from the client machine. For these fonts to be rendered successfully by the Server, the fonts used on the client machine should be added to the server font directory. If a selected font does not exist on the server, the last available font from the server folder will probably be chosen as a default. On a Windows server, this usually results in WingDings, an unreadable font, being selected and rendered.
The serverconfig.ini file installed with Map Server in C:\Program Files\Autodesk\Autodesk Infrastructure Map Server 2017\Bin has a property called LegendFont. This property is used by the Mapping Service to control the font that is used by the server when generating legend images. Please use Infrastructure Map Server - Site Administrator to change any other property settings.