A few tips for chocolate moulds are, always rest the mould on a tray before you fill it! If you don’t, the mould will bow under the weight of the chocolate and leak all over making a mess. By using the tray, you are creating a support system which allows you to move the moulds more freely and easily to the fridge.
Once you have poured the melted chocolate into the silicone mould (only fill them about two thirds full to start with) either tap it on your kitchen work surface or slightly shake the mould forward and backwards or side to side. This helps distribute the chocolate into the mould and removes air bubbles from it. You can then add more chocolate if you require in stages until the mould is fully filled.
Also, ensure you have placed the lollipop stick in far enough and add a little additional chocolate over the stick so that when you peel the lollipop out of the mould, it does not break. If there is insufficient chocolate covering the stick, it will break when you peel it out.