Hello Simone,

Thank you for reaching out and I am happy to help!
In W3 Total Cache All images converted with the Image Service tool are sent to a third-party server maintained by the W3 Total Cache team which reduces resource consumption and allows for a large number of conversions in environments where resources can be limited such as shared hosting. Images sent to the W3TC server for conversion are only held temporarily and no permanent information is kept on the server regarding the images.

WebP optimizations with the Image Service tool do not replace the original image file and all conversions can be reverted without any loss of data.

There is a possibility that something is blocking the API request from the server. When the conversion is active, please inspect the sources and check if you have any 404 requests.

Please also check if you have any security plugins that may be blocking the requests, or any other image optimization plugins.

Thanks!