The version_hash is added to the form submission by the form scripts. If that input is missing from the submission or contains the wrong value, the submission fails honeypot validation and is either aborted or marked as spam, depending on the form settings.
If the page where the form is embedded is cached, that can result in an outdated value being added to the version_hash.
If the page has any JavaScript errors, that can prevent the form scripts running, so the input isn’t added to the submission.
See the following page of the documentation about caching and optimization:
See the following page of the documentation for help narrowing down a theme or plugin conflict: