Idk about losing multiple tentacles but ive seen the occasional tip of a hammer floating in my tank figured a fish picked it off or something if theres a bunch dropping somethings gotta be wrong
Is it a mixed reef? I've had a leather coral get mad and nuke my tank. Parameters remained stable, but the leather poisoned all the corals downstream from it.
If you can't diagnose the problem you can try a big water change and a bunch of carbon.