I've seen this a couple of times. I strongly suspect that the wing hold-down bolt was not screwed into the threaded receptacle in the rubber shock mount. Sometimes the bolt misses its receptacle & screws down along the back-edge of the fitting -- gripping the edge of the plastic fitting. It looks & feels like it is properly located -- then in flight you get the lawn-dart syndrome.

You really have to be carefull with that & give the wing a good tug to ensure that you haven't made a mistake in the assembly.