Ionic applications often encounter CORS (Cross-Origin Resource Sharing) issues when using functions like `ionic serve` or `ionic run -l` to access external APIs, resulting in errors due to mismatched origins. This problem arises because browsers automatically include an Origin header in requests, triggering CORS policies that block access unless the server explicitly allows it. To address this, developers can use a proxy server provided by the Ionic CLI, which allows requests to be rerouted without an Origin header, thus bypassing CORS restrictions. This involves configuring the `ionic.project` file to include proxy settings, which define local paths and proxy URLs to redirect requests. Additionally, developers can automate URL switches between development and production environments using Gulp tasks and Angular Constants to manage API endpoints effectively. Although the most straightforward solution is to have API providers allow all origins, this isn't always feasible, making the use of proxies and automated tools a practical workaround for handling CORS issues in Ionic projects.