Pretty much proof positive one of your outside outlets is bad. About thirty years ago I stopped fooling with switches and receptacles and started using fork terminals. #6 fork X 10-12 gauge wire. Soldered terminal to wire. Why? It was after I proved to myself this superior connection noticeably reduces the temperature of the terminal and wire end. Spray protector atop the finished work and it will remain perfect for decades. Outdoors I squeeze silicone grease into receptacle and extension cord female connectors. Fillemup with grease. The increase in lifespan is nothing short of dramatic.