Event loop blocking is one of the most common performance issues in Node.js, causing unresponsive servers and poor request handling capacity. As the creator of CoreUI with over 12 years of Node.js development experience since 2014, I’ve optimized numerous APIs suffering from blocked event loops. The event loop handles all asynchronous operations, and blocking it with CPU-intensive synchronous code prevents Node.js from processing other requests. The solution involves identifying blocking operations and either making them asynchronous or offloading them to worker threads.