Over mixing pancake batter can cause too much gluten to form, which leads to chewy pancakes. Mix the batter until everything is just about combined.  Some of the recipes above suggest best ways to combine the ingredients so as to avoid lumpy batter. However, if you do get lumps in your batter, don’t keep mixing. Instead leave it to rest in the fridge for 15-30 minutes. This will allow most of the lumps to dissolve.