Hi @pako69,
Are you using Elementor Pro?
I just tested the plugin with Elementor Pro and the posts widget and I was unable to replicate the issue – different posts are loaded when you click on Load more.
Can you please install this plugin, health check: https://www.ads-software.com/plugins/health-check/
After you install and activate the above plugin it has a Troubleshooting mode which allows you to have a vanilla WordPress session, where all plugins are disabled, and a default theme is used, but only for your user – your visitors will still see the normal website.
Go to its troubleshoot mode and activate only this plugin and Elementor and see if the same issue happens with no other plugins and a default theme.
Warmly,
Mihaela