My best guess:
- this seems like a large piece, did you surface the male and female stock on the machine before v-carving each of them? slight variations in depth in the stock material (both the male and female parts) can mess up the depth, and therefore how well the male and female parts will match
- again, this is a large piece: how did you clamp the two parts together ? it requires a strong but also even pressure on the whole male insert surface after glueing