Chrome Extension gives no Access-control-allow-origin header error but works sporadically anyway

This error message is in the extension's background.js file and eventually got things to work by modifying the server code to which it makes a request. Why would it work for a while and then start showing this error in the code? I tried restarting the server but this did not seem to change anything. Is it normal for extensions that send requests to periodically retry, perhaps when the server they are addressing is down and so concluding that there is a problem?

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