Can you tell me if you can find elements with the following ids in your page: attachment-validation-filesize-configuration or attachment-validation-mimetypes-configuration? And if they exists, show me their content.
If that’s the case, it could mean that XWiki.Attachment.Validation.Code.MimetypeValidation or XWiki.Attachment.Validation.Code.FileSizeValidation UIXs are not correctly loaded.