Sounds like too little tension. NDS spokes might be un-threading themselves, also due to lack of tension. With not enough tension, the spokes micro-flex at its weakest point, j-bend, fatigue, and break.

I agree with the above poster. If your wheel was tensioned to high, it would have trouble keeping its trueness, unless a very stiff rim was used.

I would rebuild the wheel with new spokes & brass nips, tension it evenly, and stress relieve the hell out of it; on high spoke wheels, I walk on the spokes to get all the wind-up out. Use a bit of linseed oil on the threads; it'll set after a day or so and act as a very mild thread-lock.