x-cache error from cloudfront

Hello,

After filling a website form and sending it, it triggers sendmail.json 500 error and in the headers we have:

General Response URL: https://xxxxxxxxxxx/sendmail.json Request method: Post Status code: 500 etc

Response headers age: 498 server: amazonS3 x-cache error from cloudfront

What could be the issue and how do I fix it please?

Many thanks in advance