Dear Dariana,
Thank you for posting the bug report, it is already giving some hints about this issue. I read “Cannot compute convex hull for ROI Object #1 of type plugins.kernel.roi.roi3d.ROI3DArea”. I am wondering if there is something special about the 3D ROI Area you are trying to convexify (its shape for instance). I am also wondering if the plugin Convexify ROI is correctly supporting 3D ROIs.
Could you have a look at this ROI with a display block (add a block “Add rois” after the creation of the ROI to add the ROI on the sequence and a display block after the sequence to display the sequence with the ROI)? You can double click on the image in the display block to open it in a classical viewer and play with the 2D and 3D views.

Could you also upload your protocol and an example image that is causing this issue?
Many thanks in advance.
Best regards,
Marion