Yahoo has around 200 million active users worldwide and known as one of the largest web-based email service providers. Some users reported the issue of Yahoo mail not responding well, and it can be because of various reasons like the lousy internet connectivity or the third-party application you use is outdated and won't be able to support all Yahoo mail features.
Yahoo mail not responding in your device, then you need to check for the reasons that may cause such an issue and fix it in a way so that it will not bother you or restricts your Yahoo services in the future. You can resolve it by using multiple techniques like clearing the cache memory of your browser and keeping the browser or applications updated.