How to make fix constraint on the whole STEP file?

Hi,

Unfortunately I often have to work on STEP files in my company. I noticed that sometimes I cannot grouping some of the components in my model tree while working on STEP files. When I choose the components which I want to group and click the right mouse button in order to choose the group options I cannot see this option - there's no group option inside menu. I constrainted these components and then tried to grouping them but the result is the same - there's no group option inside menu after choosing components and clicking right mouse button in order to display menu. Do you know why is it like that?

Thank you in advance for all replies!