Urs nola,
Check what are the settings for the Option Switch 54 on your isogen configuration. This switch controls what welds are outputted to the ISO. To have all types of welds plotted, you should have this OS set to 0. If you need some other configuration, please check the Option Switches.pdf file (in C:\Program Files (x86)\Bentley\Plant V8i\Help\Isogen) for other possible options.
Hope this helps,
Justinas