I once flew QR with a friend to BCN. At BCN my friends bags as well as another family's once had not showed up 5 - 8 mins after the last of everyone else's bags.

My friend's lock was missing and the zipper was broken off. She didn't have much valuables (but later found her tampons box to only contain a few pieces)

The other family wasn't so lucky - zipper also broken ring box was there but ring was missing.

The QR agent on the ground refused to entertain my friend - not even when she just wanted to have a report created. He said it could be the luggages moving around in flight and causing the zip to break and such was not covered.

But it was obvious that someone in BCN was tempering with the bags. Otherwise they wouldn't have been delayed for at extra few mins at the end.