I think it was a fluke on your end since you said you "went into one thread and selected a number of items…". It sounds as if you did it properly but accidentally (?) selected an incorrect deletion option.

Well, you'll find out the next time you try it. Good luck and let us all know the outcome.

On a Mac since 1984.
Currently: 24" M1 iMac, M2 Pro Mac mini with 27" BenQ monitor, M2 Macbook Air, MacOS 14.x; iPhones, iPods (yes, still) and iPads.