It seems there could be issues when updating your site with the Update button in the manager.
If so, delete the /core/vendor/ folder and then upload it manually. You need to download the 3.1.8 release and upload the vendor folder.
Issue on Github: https://github.com/evolution-cms/evolution/issues/2048
Release source 3.1.8 on Github: https://github.com/evolution-cms/evolution/releases/tag/3.1.8
If you are too late you can simply recover it by removing and adding the new vendor folder and go to /install on your site.