To reproduce:

• open MITK workbench with segmentation plugin enabled
• load an image and create a segmentation
• right-click on the segmentation node to open the context-menu

-> Create polygon model, Create smoothed polygon model, Autocrop actions are not available

To verify I enabled the XNAT-plugin and here also the Upload to XNAT action is not available.

Maybe this is related to rMITK02a46548d2684e0c3031d023681effda6b470e86 (at least it is working with another version from October 2020).