I downloaded some parts and made a new assembly using those parts. when i open the assembly some of the parts doesn't regenerate although i have them on my PC. i click on the part in the model tree and then retrieve missing components, the assembly open. I save it and open it again, and the same issue happens.
All you have to do is save all child parts and assy in single directory / folder.
you have download all part and assembly then save in single folder without rename of part.
next you can open assembly.