This right here is actually a common issue that you can run into. In fact, with certain designs, it may happen more frequently than you want it to. So, becoming knowledgeable on how to remedy this issue is of importance to you. But, first, you should know how a lid can become stuck, in the first place. Here is the deal; with a standard three-piece design, the strainer can become stuck to the cup. This can be caused by contraction, mismatched parts or even a sticky residue on the inside of the strainer.
Either way, when this happens, here are some tips that can help loosen the stranglehold that the strainer has on the lid. Arguably the easiest method is to soak the entire unit in hot water. This hot water can dissolve any residue or even loosen up the strainer.