What I found is by removing the strips they tend to bend. If they bend ever so slightly they wont go back down very well even with new clips.
As a suggestion you might get some spare clips, and note the areas where the strip is raised up. Usually this is between clips.
Then tack the spare clips onto the roof in those areas using whichever adhesive you know will bond the plastic clips to the roof gulley. Refit strips and that should keep those suckers down.