There are two types of mouldings for the top GIMP (gap improver) rubber strip. The earlier type uses a reasonably complex metal strip arrangement that the GIMP clips into. These metal strips sit between the edge of the glass and the edge of the roof. I lost two GIMPs in short succession to this setup.

The newer type uses a GIMP that clips over the edge of the glass and has no other devices to hold it in place. It was supposedly designed to fix the problems with the first setup. It is held in place by an adhesive and mechanical clamping forces on the glass. It can be difficult to fit/remove this type with the screen installed.

I suppose you need to see which type you have (I assume you have earlier type). If you have the earlier type, from my experience the metal strips will be wavy and are therefore junk value. You will need a glass guy to fix your problem because adhesive etc did not work for me and it is a known problem, especially in hot weather.

If you have the later type, push the GIMP back onto the screen and backfill the cavity between screen and body with a strip of windshield sealant. This also stops fluttering of the GIMP and can be easily cut back when replacing the screen. My car has had no problems since this method was used.

By the way, the later setup has problems with some aftermarket windscreens - apparently some are slightly thinner than the Volvo glass and so the GIMP does not clamp properly.

Hope this helps!