I used to have the same problem on a Spez hybrid. Too loose likely. I no longer have store bought wheels or derailleurs, good riddance.
Getting locking nipples will help for sure. All my custom self built IGH wheels have them, all on heavy bikes. I also used 2.3/ 2.0 spokes on my SA hubs. NO problems now.
The spokes are way less likely to break with locking nipples too, IMO.
They do cost 3x as much of course and hardly any LBS will carry them.
Tightening a 1/8 turn more and backing off will help.